OK, starting with the bass-ics (sorry, couldn't resist), you know the musical scale? In case you don't, it's this:
A A# B C C# D D# E F F# G G# (and then back to A of the next octave)
On a piano it looks like this (starting with C in this example):- the sharp (#) keys are black
Each 'octave' comprises 12 notes - your bass guitar's thickest string (lowest note) is E.... the other strings are A D G...
Each bar on the fret board represents one semi-tone... (I think that's what it's called - either way, each gap represents the movement of one note on the musical scale shown above...
The 'open' strings on the bass guitar, in terms of the octaves are shown in bold......
E F F# G G#
A A# B C C#
D D# E F F#
G G# A A# B C C# D D# E F F# G etc...
You can go as high as your fretboard allows on the top (G) string....
Best to try playing some scales... the "major scale" is C D E F G A B C - try playing it using more than one string... this way you won't have to move your hand too far up the fret board...
That "major scale" had it's 'root' in the note 'C' (the easiest scale to play on a piano because it is just all the white keys...) The guitar (or bass) is slightly different because each 'scale' is as easy/hard as any other... if you work out the scale for any particular 'root', all you need to do is 'transpose' (or shift) that scale up or down a few notes to play the scale in a different 'key' (a scale with a different root...)
Best way, however, is to simply pick the thing up and play... you can't go wrong just plucking away and finding your own way round the fretboard...
Once you're comfortable with it, try listening to some tunes and find out what 'key' (or root note) they are in, and start playing along...
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Before you start:-
Assuming you have the right strings in the right place, you may find it easier to tune your guitar by knowing that each string should sound the same as the string below it when you have the lower string depressed at the 5th gap (between the 4th and 5th 'fret' - sometimes these are marked on the guitar with a circle or a dot of some description)... if you have a keyboard or a piano, you can tune the bottom string (lowest E) to that reference and then tune the rest of the strings using that as your starting point...
Don't worry about learning to read music from a page just yet... once you know your own way around the fret board, you will find that you can play along to and create your own music perfectly well without the need to ever 'write it down' or read it.
Ideally, the best way to learn is probably to take guitar lessons, since a bass guitar has the same first four strings as any normal guitar...