Once you have your 4th string in tune, you are going to tune the rest of the strings from there.

Play the note on the 4th string, 5th fret. Listen to the note, then try and tune the 3rd string until it matches that pitch (A).

Watch this video of
tuning the 3rd string.

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If you use your left hand to tune the string, you will have to remember what the note you are aiming for sounds like. This is difficult for many beginning bass players, so here is an option that may help. Use your right hand to tune, therefore you will be hearing both notes at the same time as you are tuning. This will let you here the "crashing" of the two notes together. As you get closer to being in tune the crashing will get further away, until it stops and you are in tune.

Watch this video of tuning the 3rd string using your right hand.

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Use the same method to tune the rest of the strings.

Play the note on the 3rd string, 5th fret. This should be the same note as the 2nd string open (D).

Play the note on the 2nd string, 5th fret. This should be the same note as the 1st string open (G).

Tablature of the basic relative tuning method

Basic relative tuning in chord chart format

This video shows going through the whole process of matching the pitches on each set of strings.

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Page 1, Tuning the 4th string

Page 3, Tuning the electric bass with a piano