Any guitar tuner will work, from the kind you clamp on the peg head to an app on your phone or computer, or this fancy Peterson strobe tuner.

Standard tuning is E A D G B E. Twist a tuning machine knob and dial in the frequency to tune your guitar.

Clamp-on tuner:

App on your phone:

Strobe tuner:

These are just a sampling of many different tuner options. Choose what fits your style and comfort zone.