You go to the BST area, find your category, ie: If you have a Mask to sell, you go to the mast part, ect ect. You make a thread like you did to start this. Type what you have to sell, note any special things that you need to tell people. Name your asking price. Easy as that. If you have anything (electronics, packs, misc.) that does not fit into the link categories, there is a one entitled "Miscellaneous Equpment" all that stuff goes there. There is also one entitled "Everything Else" that is all non PB related stuff.
After you receive a deal you like, PM the person, give them you paypal account, or what ever way you would like to receive the $ they give you the money, and their address, and you ship the item out, UPS/USPS. (USPS is cheaper)
Trading Gear is like it sounds, swapping one for one, ect. Some people will say "you add" or something along the lines of that, that is saying what I have is worth more, so you have to add, more gear, or some $.
If I think of anything else, Ill edit.
Never before has a people been more enslaved then those who falsely think they're free.