I'm assuming that's the drive belt for what is usually called the "front end auxiliaries", i.e. the various bits of machinery on the end of the engine opposite to where the drive goes out (traditionally/historically the "front" of the engine in a rear wheel drive car). It drives the air-con compressor, alternator, coolant pump etc. plus the odd tensioner/idler pulley.
The belts are made as a long tube, an inner rubber layer with the ribs to run on the pulleys, then a layer of wound cords (aramid/polyester/kevlar etc depending on spec and manufacturer), and an outer thin layer of polymer to seal and protect the cords running over tensioner pulleys etc. The cords do all the work transferring drive.
The tube is cut into belts, different widths and numbers of ribs for different applications. This inevitably ends up with the cords being cut, and occasionally you can get ends showing, which is what I suspect you can see there. If the overall belt is in good condition it is not necessarily anything to worry about, you can trim off the loose ends to make sure they don't snag and damage the belt. If the belt is getting relatively old anyway it might be worth considering having it changed, age and miles combine to decide whether it needs changing.
The belts themselves can be got from reputable motor factors like
https://www.eurocarparts.com/ or
https://www.gsfcarparts.com/ (take careful note of discount codes to use), lots of others to choose from, and are often just a relatively few ££ (maybe £10 or 15 at most usually, depending on width/length).
The cost of replacing depends on how much work is involved and ease of access, some cars can be tricky, needing engine mounts to be removed etc or going in via the inner wheel arch. I don't know what it's like on your car, others will advise.
