An EQ pedal (short for equalizer) can have many useful applications in a guitarist’s signal chain. An EQ allows you to boost the most important frequencies in your signal to help you cut through a busy live mix. It can also be used to even out differences between different guitars. Or use it as a mid-booster for your fills and solos.
An EQ is an excellent guitar tool. Remember that you don’t necessarily need to boost anything to achieve the best results. Try to cut some of the clutter that makes your guitar clash with the snare drum or the keyboards for a better band sound. You could also try leaving room for the bass player and the second guitarist in your signal’s frequency spectrum. This is what EQ pedals are for.