1992 Geo Metro 5 mph. And thats it

Engine Performance problem
1992 Geo Metro Two Wheel Drive Automatic

hi, im having problems with my car, when I drive it I can mash the gas peddle to the floor and it wont get but about up to 5 mph and VERY slowly!And when I come to a stop the engine sounds very weak like it ready to die, I dont know a thing about cars and dont have the money to take it to a machanic unless its very serious, so im wondering if its just something simple like spark plugs or something much more serious like the transmission. Please help

thank you