At the very least, it needs new tires and inner tubes, and new brake pads.
It also needs a good cleaning and lubrication of all moving parts.
You can do the work yourself if you invest in a few basic tools. You can get decent tires for $15-20 online, and tubes might set you back another $4 each depending on where you buy them. Brake pads are cheap too, but make sure you get the right ones.
The chain can be cleaned on the bike. If you plan on doing the work yourself on a regular basis, you can buy a Park Tools chain cleaner, but some cleaning fluid and an old rag will work too. Try to get all the old grease off the chain and the cogs.
You can probably get away with using the cables that you have, as long as they aren't too frayed or rusted inside the casings.
If you prefer not to DIY, take it to a bike shop and ask them to do it for you, but you'll pay a lot more than if you source parts and do the work yourself.