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 it around, or use WASD.
this is the second project I have made of this Idea, and I am going to make a final one with more bodies, I will add weapon stats that change, firing effects, and special comparability. If you want to add your own attachments and attachment points, there are comments inside of the project with instructions.