As far as specific mechanics go:
If you don't have any units, you first need to build a factory to make a unit so you can capture the nearest recruitment site so you can build a recruitment centre so you can get enough recruits to build units so you can start to expand, while also building up defences for your base. During this process you may find yourself with the mouse cursor hovering over a build button waiting for the recruit count to go up enough for you to do something.
With a starting army, you can order a couple/few groups to capture the nearest sites, and while they are moving you can build a couple factories. You don't need any new units right away, so your initial recruits can be applied to recruitment centres and your main factories. With a couple extra recruitment centres you will have an easier time cranking out more units.
In the advanced options in the lobby you can increase the recruit cost for units, which would make building slower and the starting units more important.
