My bike keeps jolting?

Is it a bike with different "speeds" - like does it have shift levers? If it does, then the shifter may be out of alignment. If not, then the chain may be too loose. If you bought it recently, take it to where it was purchased and they should adjust for free or a small fee. If not, you can fix it yourself easily - either look at the manual or go online to the manufacturer and there should be information about repairs :}