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.
i always assumed that was a resupply pod or something, but you're right, its an allegiance subverter. why the heck is there a picture of a subverter on the "use component" button?
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...the green, sticky spawn of the stars
(with apologies to H.P.L.)