There are few ways to tune a guitar. Having a tuned guitar can make a big difference on how it will sound when you play. Experience guitarists can just tell by the sound of a chord whether the guitar is properly tuned or not. Some people are good at recongnizing the changes in pitch, but this is something you can learn by practice. Training your ear is very important if you want to play with other people. You can tune the guitar by:
I am assuming that you can tune the guitar when the note is played. This is quite handy as it can play to note or tone continiously. You can set the delay and check all string in order. The second box metronome is used to keep the timing. You can even set some beats to play the songs with rhythm.
Learning a correct sense of timing is one of the biggest step if would like to play with other people. Being able to feel the beat and timing is essential to playing songs and riffs. If you dance to a beat or have played any percussion instrument banjo, table, drums (also banging desks in college) you will have a sense of rhythm. The difficulty becomes how to keep up with speed while changing notes and/or chords in the begining. Always practice with a slower tempo and start increasing once you become comfortable at the slower pace. Metronome is quite useful to keep track of timing when you busy figuring out the notes and positioning your fingers to play. Below is a metronome you can use to keep the timing. You can even set some beats to play the songs with rhythm.
Simple Drum Beat