Alpha Channels (Sorry if I Spelled Wrong)

Hey, I am a noob in texture.
So I wonder.
What is the alpha channel for.
And, how or why should I make/edit it.


I guess there is more wondering this.
(Yeh, I forgot the search thing here but...)

when you are making a scope you use the alpha channel to tell the game what is gonna be visable and invisable. and when you make guns you use it to make shine kinda thing, fx if you are making a gold/silver then its very important to use alpha

So more, alpha in guns are better.

Do I color it or what do I with it?


Thanks for answer anyway