Resources & Budgeted units

you can add a resource if you set the default/units per time equal to 8 for 8 hours per day then

what it will do to get the manhours or budgeted units it wil take the duration multiplied by 8 hours per days

so a 5 day activity it would the budgeted units would be 8 hours per day Times 5 days or 40 hours or 40 budgted units. 

this means 1 man for 5 days = 40 hours

you can override the budgeted manhours and or you can put in the units/time in the resource for example you can put in 16 instead of 8 and the budgeted units wil now be 80 hours or 2 men for 5 days.