In the Stack Exposure column, uncheck any stack types you don't want to play.
Each row is one stack type. In NFL the layout is the QB plus how many players from his team, then a line, then how many players from the opposing team. So QB + 1|1 is QB plus one teammate with one bring-back. Uncheck the ones you don't want. Or click Select / Unselect All to clear everything and check only the types you want.
Some sports also list secondary stacks, which are stacks without the QB. Secondary 2 is two teammates without their QB. Secondary 1-1 is two skill players from the same game on opposite teams.
Other sports lay it out differently. MLB shows hitter stacks like 5|3, 5|2, or 5 with no second stack. The rows always reflect the common stack shapes for that sport.
If you want to control which positions or teams can be inside a stack rather than which stack types you play, that takes a stack rule.