I move a colony ship into a system with an M-class planet.  Now... what do I do?  I want to colonize it.

I'm stopped dead in my tracks as far as trying out this game.

First,to tap your colony ship,there should be some options you can choose around the bottom corner.Select the "Single turn Action",then there should be some more options you can choose,by then you should be able to find a "colonize" button,however :   

If the M class planet you see is red,then it needs to be terraformed 

if its green then you already own the said planet  

it needs to be grey/white,then you maybe be able to colonize it