Hi, I recently bought a track bike of someone.
When I was putting the rear wheel on yesterday, I noticed that the wheel doesn't rotate on the axle, however, when I loosen the nuts on the axle it does. I'm completely new to all this so I'm not sure what's meant to be where and how tight/ how loose and what not.
Any advice would be great, I really don't want to damage the bike.

Cheers!

The axle nuts on the hubs are probably too tight. They need adjustment to rotate freely, it's fairly easy.

Read this:
https://sheldonbrown.com/cone-adjustment.html

that sheldon brown link is good for understanding the what's meant to be where.

regarding how tight/how loose - you want it tight enough that the axle is not knocking around but loose enough that it spins freely. This balance is very possible with a properly greased system with quality parts. The problem is that worn or cheap axles and nuts and cones will make it nearly impossible to find and lock down the perfect place.

When you talk about loosening the nuts - are you talking about the axle nuts? - not the lock nuts? If that is the case your locknuts and cones are probably loose and the axle threads might be stripped or damaged.

You can monkey around with it, trying to get the adjustment correct, but I would recommend taking the whole thing apart.

The first question asked should have been they type of bearings you have, figure that out too.

Thanks! I also noticed that part (sorry I really should know what it is) about the lock ring isn't sitting straight. any advice for that? Thanks.

The part that's crooked is just a bearing cover and most likely has no effect on how freely your hub spins. You can most likely tap it back into place pretty easily.

Brilliant. Thanks for the help everyone, seems it's running okay now. It was hopefully just because the axle buts where too tight, where the previous owner had removed the wheel and tinkered with it before he handed it over to me. Thanks!

Looks like the previous owner quickly greased the hub before turning the bike over to you, but did a sloppy job. First, the dust cap wasn't seated propertly, and next, the locknuts were probably not tightened enough and ended up too tight when the wheel was put back in, which is what you noticed.

Luis