Step 1: Getting A Guitar
If you have an electric guitar you will need an amp and lead (see pictures) but whatever you have you have I would recommend buying a plectrum (A.K.A pick) choose a medium or light type as they are most suited to beginners.
You could also get a tuner but they are not totally necessary (see next step)
Step 2: How to tune your guitar
You will need to know which string is which in order to tune the guitar so the strings from thinest to thickest are:
1st string (E)
2nd string (B)
3rd string (G)
4th string (D)
5th string (A)
6th string (E)
Sometimes you may have to drop tune your guitar this is quite easy to do you simply tune the 6th string to whatever note the drop is, e.g. for drop D you would tune the 6th string to D.