plundering

You would "strip-mine" ore by clustering planets (If your picky only ones with high ore 800+ etc), and building just enough pop to build mining on the planet. Mining ore happens when you spend turns, and it will go faster depending on how mnay mining building are on each planet / cluster.

Once the ore is removed, it can be destroyed and used or sold.

To Mine minerals
That is done automaticlly each time you spend turns. the rate this happens at depends on TWO things only.
1) Mining research
As it states it increases the amount removed by 10% each level
2) Race stats
In the manual (Up top on the left, kinda hard to see lol) each race has a list of race modifiers, that change each aspect

Any more Questions feel free to PM me or make a new thread :)

Plundering ships will only increase income by reducing the upkeep your paying (See your income screen for a breakdown of that)

Most races plunder planets just because they dont want to keep them, if you are making clusters, you will grow a lot more efficantly keeping the larger planets and plunding away the smaller ones.

Or if you were making some quick cash by mining all the ore and selling them, you can explore, cluster mine then plunder :)

Hope this answers your question :)