ACT!'s opportunity functionality is arguably the most powerful of the ACT! features. Fortunately, even though it's capable of handling very complex processes an Opportunity record works in much the same way as the Contact, Company, and Group records do. And, if you feel comfortable with those record types you're bound to feel right at home once you start working with Opportunity records.
It would probably help if some nice person had already added a number of opportunities to your ACT! database. However, if you find yourself diving into a database that is devoid of opportunities you might want to open the ACT! demo database that automatically installed when you installed ACT!. The demo database has already been populated with a number of opportunities.
Normally when you make a selection from the Navigation bar ACT! opens up the detail view. However, when you choose Opportunities from the Navigation bar the opportunities automatically display in list view. If you are viewing an opportunity in the detail view and then navigate to another area in ACT! you will be returned to the detail view if you choose Opportunities from the Navigation bar.