[God Emperor]

As a recently graduated newbie, I know where you are coming from but can help.

Think of weapons platforms as planetary defence bases.
You build them on a planet and they take up cargo space. Ships with cargo bays can move them around (use transfer cargo command). Therefore, a colony ship with a cargo bay could carry a certain number of WP's.

You design them in the Unit Create menu.
They cost no maintenance but cannot be upgraded. When you want to get rid of them (to replace them with new ones), you use the jettison cargo command.

Early models should be equipped with missiles until you get decent projectile or beam weapons. Fitting them with sensors and armour is useful, but, I'm not sure about shields.

Their only use is defending planets. They are very useful at supporting defensive fighters and ships. On their own though, they are not so good as enemy ships can move in, fire weapons and retreat out of WP weapons range. Individually they are more useful than satellites and bases for defending planets, although satellites can be better if you have dozens of them (which is possible because once launched into space, they dont have a cargo limit).

Hope that helps.......