Welcome to the forum... and another Aussie? If so, where did you find the book in Australia?
You get to activate one figure each turn, but if the figure you activate has the command rule, you get to nominate two other figures within 10" of that figure with Command (see p25).
Thus you can choose to activate one figure, or up to three using a figure with command. This is a good reason to protect your leader.
You don't have to nominate your leader figures, but unless you have another figure with the Lieutenant skill, you will only move one figure per turn.
Note also: Alert on p21
Once all the figures you have activated (a single figure, or up to 3 using command) have had two action, the turn goes to your opposition.
You don't have to activate figures that haven't moved in previous turns if you don't want to.