I often fix up thrift store sewing machines. Don't sew very much on your machine until you clean and oil it!
The top will come off in some way. Usually there are a couple of screw you can undo to lift off the top. Put a drop of oil anyplace you see an oil hole plus anyplace where there are two parts moving against each other when you turn the wheel.
The left side cap should swing away backwards. On some old machines these are held in place by screws like the top. Again, oil every part that moves when you turn the wheel.
You should also dis-assemble the bobbin area, use a stiff brush to get out any dust, oil the bobbin race, and re-assemble.
It's also a good idea to unscrew the metal part that surrounds the feed dogs so you can remove any lint that may have accummulated in there. If you can see any moving parts, you can add a drop of oil there too.
If you find a small red or white piece of felt in the bobbin area (be careful to not mistake it for lint!), leave it in there and add a drop or two of oil to it. This is an oiling wick.
Once the machine is completely oiled, it's a good idea to remove the needle and run it at max speed for 1 to 3 minutes to "burn in" the oil. Don't force it. If the machine does not want to move fast, I will run it lower for a minute or two and then let it rest for a day before trying again. Sometimes the oil needs some time to penetrate.
These old machines are worth fixing up because they are such workhorses!