keyboardmashing

I'm sorry if this has been asked a million times - I couldn't find a search function.

My rear gears on my Diamondback Edgewood are doing some weird things:
-It seems to think that gear 2 is gear 1
-It pops from gear four to gear six, skipping 5
-It won't go into gear 8 at all

I don't really think that the gears are worn down much (although they are on the other set, espc gear three), and the is little to no grease. There must be something wrong with the gearing system itself if it doesn't even correctly know what gear it is in. When it's in gear 2 thinking it's gear 1, I try to put it in 1, but it won't stay.

Any suggestions?

Al1943

The rear derailleur and/or cable is badly out of adjustment. Or the rear derailleur or derailleur hanger is bent.
Check to see if the derailleur is in proper alignment.
Use the derailleur setup and adjustment instructions found at www.parktool.com.
If you are not sure about the condition of the hanger take the bike to your local bike shop.