Squaddies are the ordinary soldiers in the army.
Squaddies are the regular soldiers who do the main work in the army.
Examples:
The squaddies march in a line.
The squaddies eat together in the mess hall.
The officer tells the squaddies what to do.
The squaddies clean their boots every day.
The squaddies are very brave in battle.
The squaddies help each other a lot.