For each task, in details window, select resources that will accomplish it and fill in the units of the resource-task assignment.

For human resources, the Units coefficient shows the part of its working program dedicated to the current task (e.g. if the resource have an 8 hours per day program and you set 0.5 units, the resource will spend 4 hours per day working at that task).

For materials, Units gives the quantity (number of measure units) needed to complete the task.