Keys

Killaqueen!!!

This may seem like a stupid question and maybe I've gone about the wrong way of writing a song if I don't know this, but....

How do I know what key a song is? Will a song always be in the key of something? I suck at writing songs but I'm only beginning and I have some simple chords put together in a song and I want to add a solo (or even just a short lick) so how do i go about doing this if the key is, for example, A major? Would I just use the Amajor scales up and down the neck (whatever they are) or are there loads of scales to chose from? How do I know which ones will fit?

There's a lot of questions there because I know I need to look up on my theorey but if anyone would like to give me a short answer to even just one of those questions it'd be great!

Cheers

-=al=-

once u get a grasp of some simple theory on scales key sigs etc it comes to u, u eventually hear what the root note is hear what chords and intervils are being played, ear training is quite usefull for al this kinda thing, once u find a few notes in the song/chord progression u can find how many sharps/flats there are, which are a nice insight to figuring out the key

Rustar

You need to be able to hear the intervals first, yes.
What I do is one-string it til I find the famous 3-fret stretch of the minor pentatonic. Once I've found that, I play the entire minor pentatonic and see if it fits. There are two '3-fret stretches' in every scale, so if it doesn't sound right, I try the other one.
Once you've found the minor pentatonic that fits, the third note up in it is the key if the song is major sounding, or the root of the pentatonic is the key if it's minor sounding. Quick way to play along with almost any song!
Of course, some songs have 'chorditis' and change frequently, so they're harder to figure out. Especially if the song does a lot of modulating.