I'm no mechanic and perhaps lack the correct terminology, but this is a V-brake (or linear-pull brake) and you might just need to lock in the "noodle" (the metal housing) back into the other arm's stirrup, like that ... at least that's what is apparently wrong on the picture you've sent.
I don't know if there are other issues but this at least puts your brakes in the correct neutral position - would be great of you could get a more detailed shot to assess what is broken/missing.
As many other users have noticed, the brake arm on the picture's left doesn't right
- I don't see a brake pad, and that's a very essential part of a brake
- The arm should pull away from the rim by itself if you unhook the noodle but it sits on the wheel, which indicates that something is broken there, too
- As pointed out, the cable is frayed, too, which might lead to it failing under load - and you clearly don't want that, especially on bicycle's front brake.
You might ask your friend what happened to the bike and if he still has any of the bike's parts, like the apparently missing brake pad, but my educated guess is that the bike has been worked on but then given up in the process. Frayed cables without end caps often appear when somebody without the proper tools fixes a bike, so I would definitely take it to a shop for repair and getting everything set up as it should. At least if you want to bring the bike back to a safe and rideable state. Even if the LBS decides to swap out the full brake for completness (or due to damage to the original) one, it's probably not a very expensive job. New cables, a cheap V-brake probably doesn't cost much more then 15€ and a bit of work.