Which Scope

[RoxboroRedneck]

I have recently accuired an AR-15 and I am serioulsy considering putting a scope on it. My problem is im a complete noob when it come to scopes. Most of the shooting I do is at a range, typicall around 100-150yards. SO I was just wondering what would be a good scope? no wanting to spend more than ~$125 if possible.
My 2nd question, how does a scope hold to a picatinny rail? Is it with normal rings or is it something else?

 

[MachIVshooter]

If you're willing to go $150, it is tough to beat the Nikon Pro-Staff 3-9x as budget scopes go. You can get Weaver rings for $15 or $20.