Scouts

Scouts (9 (or 2 in the European version)) are the weakest movable piece in Stratego, besides for the spy, but they can move any number of spaces in a straight line, and even attack on the same turn. It is usually best to have scouts where they are easily accessible, although scouts can come in quite useful later in the game as well.

Strategies
Scouts are mostly useful for 4 different things: Scouting, bluffing, flag scouting, and spy scouting. You should generally try to save some scouts for each of these tactics, as you may need to use them.