on "cleanliness 0" click on the grey dots to select an attachment point. next, click on one of the 3 options to attach it. if you want to put something else on, click on the attached object to remove it, then click on something new. to remove the grey dots, set "cleanliness" to 1. press/hold space to move the thingie.
I was heavily inspired by what little Escape From Tarkov content I had seen (quite a few years ago now). I had a few pieces of paper with drawings of stuff like this on it (though far more into detail with what you could change, but not as realistic). If you want to add your own attachments and attachment points, there are comments inside of the project with instructions.
