Hello DRA!
I hope you are enjoying the liveaboard experience!
First off ... it will be helpful for you to do some reading to understand the terminology. Pulleys on a sailboat are called BLOCKS. The sliders that you reference are called TRACKS. Follow thru on learning all of the rest of the terminology and it becomes easier to communicate. Also, purchase Don Guillette's sail trim guide and charts in this store for a very quick, understandable education in sail trim. It is invaluable when you are learning.
The blocks that you have on the track along the toe rail are also called fairleads for your jib or genoa sheets (lines or <rope> that are attached to the clew of your headsail). The button on the fairlead is a pin-stop that is used to adjust the fairlead position, which is something that you should learn about. I'm a little confused by the configuration because it appears that the winch (with blue cover?) and cleat seem to be in a weird configuration relative to one another - I'm sure it is just because I can't see the entire assembly relative to the boat. The sheet from the headsail clew passes directly thru the fairlead on the track and then typically back to the winch with a cleat behind that to secure the tail end of the sheet.
The block that is deck mounted appears to be an add-on feature, perhaps installed by the previous owner. They will trip you if you don't watch out. This appears to be a deck-mounted fairlead for your headsail, that you would use instead of the fairlead on the track. I'm assuming this block is further forward than the track-mounted fairlead, so it is intended to be used with a smaller headsail (non-overlapping), and it will draw your clew further inboard for tighter pointing (tacking) angles. Fixed-mounted fairleads are not the best because the position gives you very limited control of your sail shape when you are sailing. Basically, you can't adjust the sail shape for optimal performance if you can't move the position of that fairlead. But they are not uncommon on small sailboats with simple systems.
I would check below deck to make sure these are mounted with a backing plate to be properly secured. Any screw or bolt penetration through a deck is a potential source of water that can deteriorate the core of your deck. The earlier you start to pay attention to these fasteners, the better off you will be.
You also have a pair of blocks that are mounted to the coach roof at the handrails. These also may be an add-on. The purpose isn't clear. They may be used for even tighter pointing angles with a small non-overlapping headsail. They may also be used to bring lines back to the cockpit from the mast (if you don't have deck organizers).
Nobody says that you have to rig your sailboat exactly in accordance with the plan that is provided when the boat is first constructed. It is very common for people to add blocks, deck fittings, winches and cleats to set up the rigging as they prefer. First you have to learn how to sail your boat, then you will start to consider modifications.
Your traveler track appears to have a simple car that is set on the track with pin stops that are used to adjust the position. Your mainsheet block and tackle assembly should be fixed to the traveler car when you set it up.
