After your boat tells you what to do, it's time to explore Windfall.
If you didn't buy bait before, now's a good time. Beedle's ship circles the island. Get the bait bag if you don't already have it, and remember to buy a few hyoi pears.
By the way, if you bother the pigs too much, you'll get killed (like with chickens in previous Zeldas).
If you don't have a lot of money, the pots around town conveniently have plenty of rupees in them.
Buy a Sail
Your first stop is to the guy in the corner of town behind the counter who wears a hood (Zunari). Talk to him and agree to buy what he's selling, and you'll get your sail.
Get Tingle out of Jail
This part is optional. Go into the door behind the disco guy dancing by the gravestone. Talk to Tingle if you wish, then break the pots to find the switch to open his cell. He'll give you the chart to his island, and the Tingle Tuner, which you can use if you have a GBA and a GBA-to-Gamecube cable.
If you know about the gallery side-quest already, and want to complete it, be aware that you will need to use the Tingle Tuner in order to get all of the figurines. If you get all the figurines except the one you need the Tingle Tuner for, you will still get the prize for completing the gallery.
Get the Picto Box
Now, head into Tingle's former cell. You can get 5 rupees under the bed. Move the box to the side by standing next to it, grabbing it with R, then moving the D-stick. Crawl into the hole, then press up on the C-stick so you can avoid falling into a trap. There are trap doors that look like wooden planks on the floor. Don't crawl onto these.
The quick way through this maze is left, right, left, right, straight three times, right, straight three times, and right again.
At the end of the maze is a chest containing the Picto Box, which is required to complete the figurine gallery side-quest. Once you have that, go back through the maze into the cell, and go outside.
Become Lenzo's Assistant
Now take the ramp going up to your left, go through the arch to your left, and look along the left wall for a door with a camera above it. Go inside and talk to Lenzo. Go up the stairs in here until you reach his gallery. Look at all the pictures, then leave. Now go back in, and agree to try to become Lenzo's assistant.
For your first task, go stand on the pier by the sailor and face the postbox. Wait for a while until a man in red walks through the arch, then get out your picto box. He'll be putting his letter in the postbox soon, so don't waste time when you zoom in. You need to be zoomed in enough to see the red guy's whole body plus the postbox. Make sure that he isn't too small in the picture. As soon as you see he has the letter in his hand, take the picture. If you're not fast enough, the letter won't be in his hand and the picture won't count. Take the picture to Lenzo and show it to him by using your picto box while in front of him.
Next, go into the coffee shop above Zunari's store, walk up the stairs, and pick up a jar. Stand as far away from the guy at the table as you can without letting anything obstruct your view, and throw the jar at him. Quickly take out the picto box and take a picture while the guy is shaking. Take the picture to Lenzo.
The final task is tricky, but you have to do it if you want to do the figurine gallery sidequest. Go outside Lenzo's shop and you'll see a woman in an orange dress named Linda. Walk up so those kids are circling you, but don't get too close to Linda. Get out your picto box. Set it up so that Linda will be on the left side of your picture. She should fill about 3/4ths of the frame. Now wait around a while. Eventually, a guy named Anton will walk up the path to the right of Linda. Zoom out enough so that Anton's whole body will be in the picture, and wait for him to walk past her. When Linda and Anton look at each other, make sure none of those kids are in the frame, and take the picture. Don't worry if you don't get a chance the first time, because they look at each other a second time. When you have the picture, take it to Lenzo and he'll make you his assistant and give you a Joy Pendant.
If you go out and back in again, you find out that Lenzo's first job for you is to get a firefly. We'll do that later. It's one of those tasks necessary for the gallery side-quest.
Play Hide and Seek with the Killer Bees
Next, we will play hide and seek with those kids who hang around in front of Lenzo's shop. First, go into the door near Lenzo's shop that has a chalkboard next to it, and talk to Miss Marie until she asks you to talk to the boys. Now go out and talk to the kid in the hat. Agree to their competition.
First, go around the side of the bomb shop, sidle across the ledge, and check behind the building. There's one kid. Follow him, and keep doing a rolling attack toward him by holding A while running. Keep doing this until you catch him. You'll have to do the same for each kid. Remember to actually catch them after you find them. Next, go to the tree near the postbox and roll into it. There's another kid. Now go behind that gravestone to find another kid. Finally, go through the arch to the left of Miss Marie's school, and check behind the bush for the last kid.
You get a piece of heart. Now you can get some rupees, but if you already have close to 200 rupees, don't do this part until later. Go in and talk to Miss Marie and she'll give you 50 rupees. Go back out. The kids will talk to you about giving Miss Marie a Joy Pendant. To find it, roll into the tree next to the bomb shop. Then go back and show it to Miss Marie (with Y, Z, or X) to get 20 rupees.
There's a battleship game in the building facing Miss Marie's. Once you win, you get a piece of heart. Win again and you get treasure chart #7. If you beat the high score, you also get treasure chart #23. If you run low on rupees, see the previous section for how to get some rupees from Miss Marie if you haven't done that already.
If you go up the staircase in the courtyard and go through the door, go over to where Mila's father is walking, climb up on the rail, and drop (don't jump) down from there, there's a chest up on the auction platform with 20 rupees in it.
Now you can leave. Get in your boat and turn until you're facing the direction the arrow behind your boat is pointing. You can cruise out of this little enclosure by holding R, which makes you automatically go forward. Press left or right on the D-stick to steer. Then use the sail to get going. Just keep going until you automatically land.
By the way, if you see any seagulls flocking in the air on your way, avoid them. It means there's a big octo hanging around there, and there's no way you can beat it at this point. Also avoid funnel-shaped cyclones, which warp you to a random spot on the map. Also, if you see a narrow boat with guys in diver's masks on it, talk to the head diver guy to receive treasure chart #34.