Help Please, Car Shakes, Rmps Drop, When Driving Jerks

Ok, it started happening 2 days ago.. When standing at lights or just turning the car on in idle, the rpms drop and jump from i'd say 500-800 , when driving sometimes it's ok, but soemtimes when i'm driving uphill it feels like the engine is going to jump out. Also you can hear from the ouside the jerking of the car b/c of the exhausts. I'm sorry if this explanation is not good, but i reall don't know too many car termins and english is not my language, so excuse me. What else. I went to a mechanic he has no idea what the problem is but he told me for 250$ he can definately eliminate it. but i really can't just throw this money right now. Can it be the spark plugs, if yes, where are they located, becuase deffinately different from some other cars becuase i can't locate them. And what might be the problem and how can it be eliminated...Thank you very much!!

P.S.- is it even safe to drive like this?

Thank you
-Eugene-