Good post above. I'll just add the following:
Let's say I hear a new song being played or created and I want to play along on the bass to that song. What information, at minimum, is needed to play along correctly?
Fiirst what is the key this song will use. Your ear will kick in, but, until it does use chord charts or fake chord sheet music - Google search words, Chords, name of the song - or ask the keyboard player or rhythm guitar what key we will use for this song. Here is one in G.
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Or run the C major scale and when your song sounds good with one of notes in the C major scale - look down and see what note that fell on. That is the tonal center, aka, your key for this song.
(And what information, ideally, is needed? For example, playing in D with a D song and not "hitting the wrong notes." How do I know what the wrong notes are and what the right notes are? How do I know what tempo to play?
If in D your notes and chords will probably be from the D major scale. So gotta know what those notes and chords are. I relied upon the major scale box. Place the D on the tonic (root) note of the pattern and find your notes within the box.
Major scale box showing scale degree numbers and the root note on the 4th string.
G~~|---2---|-------|---3---|---4---| 1st string
D~~|---6---|-------|---7---|---8---|
A~~|---3---|---4---|-------|---5---|
E~~|-------|---R---|-------|---2---|4th string
D scale = D, E, F#, G, A,. B, C#, D
Scale # = 1, 2, 3, ..4,..5 ,6, .7... 8
Place the R on the D at the 5th fret. Notice your I chord {D} is on the A string 5th fret. The IV [G] is above it one string and the V {A} is below it on the E string. I-IV-V all in one place.
What exactly is BEADG, etc.? Why is a downturned E string a D but the string higher than A is also a D if it's higher? Noob questions, I know. But I'm a noob, so I'm asking.
BEADG is a dropped D tuning. Right now a can of worms, best left alone... When you get with a band that uses Dropped D then you can start using it, but, IMO now is not the time as all instruction material is in standard tuning.
Alternate tunings make it easy for someone to do something. Dropped D is probably one of the first you will run up on. If my memory is correct dropped D lets the guitar make power chord easier. Alternate tunings right now in your journey IMO are a can of worms that do not need to be opened just yet. I played standard tuning all the time. and had no problems from doing so. Suggest you do likewise until you get with a band that uses dropped D.
Good luck.