When I try to shift into 5th gear, my bike starts to ride with a jerky motion. It makes a screeching sound too. How do I go about fixing this problem? I know this probably sounds like a stupid question to you all, but I'm a newbie to bike mechanics and I could really use the help.

hmmm....

have you checked for a rabbit with a pancake on its head?

perhaps you culd give us some more information, such as precisely where the screeching sound comes from, and where the jerking originates.

A dry pulley bearing can make a high pitched squeal/squeak/screech sound. A little grease on the bearing sleeve fixes it up.

The jerking comes from the chain, and the screeching comes from the same area. And I'll check the pulley bearing like supcom said.

EDIT:
The jerkiness is constant after I switch gears.

Is it because the chain is dragging on the front derailleur side rail(s)?

Hoist the back wheel off the floor, and then turn the cranks by hand while you try and shift into 5th gear. Then you will be able to see what is rubbing or skipping. If this is a 5 speed bike, the rear derailler limit screw may not be letting the derailer move all the way out, so the chain doesnt drop onto the 5th spocket properly. Do a search for the Sheldon Brown and Park Tool websights to get all the details of gear shift adjustment.