How does "Preassign these teams to the 1st through 4th week of every month" work?
Once you have created two or more teams for a given shift time, this option will appear on the right hand side of the window. Turning this option on will always preassign your first team to the first week of the month, your second team to the second week of the month, and so forth, up to potentially your fifth team serving the fifth week of the month.
If you have less than five teams, then no teams are preassigned for any weeks in the month that correspond to the missing teams. For example, if you have three teams, they will be assigned to the first three weeks of the month, and any empty positions for the rest of the month will be filled in normally by the automated scheduler with the volunteers or teams that have had the least chances to serve in the past.