How do I know what troops to have with what heros I just started playing this game?

Check your hero. When you select them in the Hero page, on the top left of the screen (beside the hero) it will say something like "Archer" or "Universal" etc.

If you see "Archer" then obviously that hero is best suited for archers (gives attack and defense buffs to archers only). You can check their skills and see exactly how much boost they give to their preferred troop type. If you see "Universal", then that hero can be placed with any troop type, be it cavalry or archer (their skills are also universal and boost their troops' defense or attack regardless of type).