This article explains how to switch back and forth between forecasts and actuals for assignments.
When you bring up the Resources->Assignments or Projects->Assignments pages, the default value type (shown as the Forecast button in upper right of page) is Forecast. Thus, each row on the grid 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.
The third option on the toggle is Costs. This will show you labor costs for the assignments on the view. Costs are calculated as follows:
If you have a monthly rate, let’s say $10,000/month: The calculation simply takes the monthly rate and multiplies by the monthly FTE demand. So if you were forecasted .75/month on a project, the labor cost would calculate to $7,500 per month or $90,000/year.
If an hourly rate, the cost is calculated based on the assigned hours (or FTE converted to hours) times the rate.
See Understanding Labor Rates for more information on which rate is used.