Select Sales on the left hand nav
Click Opportunites
Click New Opportunity in the right hand corner
Input the missing details:
βClick Opportunity Impact to see how this change would impact the existing forecast
The change is shown in Green
Click Create
Now, you'll see each of your opportunities on this view and can use filtering as needed
Use the Actions on the right side of the opportunity to Edit, Confirm, or Delete
To configure if Opportunities should be shown in the forecast:
If you select for Opportunities to impact the forecast the changes will be hi-lighted in yellow