MH normaly fight with long Gallic swords in an infantry formation (some space between individual soldiers). The Spear is a secondary weapon, you have to press ALT for them to use it.

I am using them in my Aedui campain, they are cool, but they are not too strong. For some reason, they tend to take heavy casualties to javelings. Because of that I rarely put them in the front. I generaly use them in HOLD and make them fight with spears to hold off cavalry.