When you bring up the Resources->Assignments or Projects->Assignments pages, the default value type (shown in upper right of page) is Forecast. Each row is showing the Forecast for the assignments.
When Forecast is the value type, you can view, enter or modify Forecast for each assignment you have the appropriate rights for.
To toggle to Actuals to view enter or modify Actuals, click the button currently showing Forecast and it will change to Actual, with the values now shown being the Actuals for the assignments.
The Entering and Modifying Labor Actuals section explains how to enter and modify Actuals on that page.
Toggling the button now showing Actual will return the value type to Forecast.