Picks or Plectrums

A pick or formally called a plectrum is a small piece of plastic that you use to play the guitar.
You can use your fingers by themselves and not use a pick as well.
I recommend you start with a pick, but do try you fingers in the future.

Tuners

Tuner – always make sure the guitar is in tune before playing it. 
Warning – if the needle to far to the right – loosen the string or it will break.
There are two types small portable and foot pedal.

Metronome

Practice play with a beat, a metronome is required to practice timing.
Boss makes a tuner and metronome combo.

Drum Machine

A drum machine can also be used and is a little more fun to practice with.