What do you need to adjust?
If it's the shifter, you should see an arrow in a window on the silvery cast zinc bell crank attached to the right end of the rear axle. The arrow should move when you operate the shifter. Put the shifter in second and the arrow on the bell crank should be between two red lines.
If not, the adjustment is made where the cable enters the bell crank. There is a device called a barrel adjuster. It is like a bolt with the cable housing going through its middle. There is a nut around it, just before it threads into the bell crank. The nut locks it in place. Loosen the nut, then thread the barrel adjuster in or out of the bell crank until the arrow is between the two red lines, then hold the barrel adjuster in place while you tighten the locking nut.
If the hub makes noise when you brake, then it needs grease. It's a special Shimano grease and is added by rotating the chrome steel cup covering the left end of the hub, outside the spokes, counterclockwise and squirting it into the hole which appears.