To view the overall workload of a project's resources, go to the project of your choice.
Go to the Gantt tab, then activate the load switch.
The figures that appear represent the total remaining capacity of a resource in hours for a given day (if your Gantt is set to day mode).
Remaining capacity is calculated as follows :
For a given day : Daily capacity - workload : Remaining capacity
To modify the workload, you can edit from the Gantt the number of hours allocated to resources for their tasks.