Clean the bearings, if they're in good shape, you can re-use them. Here's a shopping list:
cone wrench combo, 13,14,15,16mm
Shimano freewheel removing tool
1 rear axle 10x1mm threading, measure length of existing axle 1st
You'll want to remove the freewheel, clean off the bearing races & cones and inspect for smoothless. Take apart axle, cones, washers, spacers and locknut. Pay attention to order, I tell people to draw a line on a piece of paper representing and axle and lay the parts down in the exact original position.
Install axle cone, washers, spacers & locknut on freewheel end of axle. Tighten down locknut. Apply grease to both hub cups, drop in bearings. Push through open end of axle. Install cone, washer, spacer locknut on the other side. Adjust bearings so you have a tiny bit of play. Tighten lock nut. Install freewheel and you're done.