Depending on your Sim's skills, career, and situation, your Sim might get offered an opportunity. The requirements vary, and might include collecting an item, reading a book, upgrading something, going somewhere, and so on. The rewards also vary. Skill-based opportunities might reward you with a boost of a particular skill, or they might open up new abilities based on the skill in question. Career opportunities might reward you with improved job performance, improved relationship with boss, and so on. Below is a list of all opportunities.
If you are ever unsure about the requirements of an opportunity, go to the opportunities tab (marked with a star) and highlight the appropriate opportunity category (career opportunities are marked with a desk icon, skill opportunities are marked with a hand and wrench icon, and special opportunities are marked with a star). If you have accepted an opportunity, the icon will be colorful, and a description of the opportunity will appear in the text box. The text box will tell you when the deadline is, if any.
When you have highlighted an opportunity this way, a pop-up text box will appear above the lifetime wish area. This text box will have a button in it if there is an action that your Sim can perform right now to complete the opportunity. Note that some opportunities can only be performed between certain times of day, and if it is not during that time, there will not be a button to perform the opportunity, but instead there will be a general description of what you must do.
Similarly, if there is no specific action that your Sim must perform to complete the opportunity, the pop-up text box might display information about your Sim's progress on the opportunity. For example, if a Sim must collect a certain number of items, or perform a task for a certain length of time, the pop-up box will show how many items, hours, or whatever, have been accumulated so far for this opportunity.