When the game first begins, the little players will come out on the field and line up. Then the game will actually start, and you’ll see them in formation.
There are different formations, some of which are preferred by different teams. All of the teams have a default formation, and when you are playing against them, that’s the one they’ll use. (The default is different depending on what team you’re playing against; for example, Maraqua uses the 1+3 formation, whereas Roo Island uses the 2+2). The team you play for, that is, the one that you control, will use whatever formation you tell them to use. I personally have played for Maraqua, and found it easiest to use the 1+3, but you should experiment and find out which one you like the best. You can also play from left to right or from right to left; this is also a matter of personal preference.