[Suicide Junkie]

Yes. Weapon Platforms go on planets, in thier cargo. During combat the planet will have weapons, shields and armor, just like a ship/base would.
Note that platform shields act like armor.

To use components, there are two places. There is a stellar manip button, just above the NAME button, and left of the scrap/retrofit/analyse button.
There is also a component USE button to the right of the cloaking buttons. It looks like an allegiance subverter with a bright green dot in the bottom right corner of the button.