Controls:
Left mouse - move
Right mouse - interact/grab/release
Hold [Right Mouse + Shift] - fast grab
Hold [Right Mouse + Ctrl] - fast release 

Items:
Crops - sell on other planets
Water - needed to grow crops
Seeds - needed to grow crops
Fertilise - speed up crops growth

Mechanics

1. Apply items to a planet.
Just carry an item so it appears above a planet and release
2. Grow crops. 
You need to apply seeds and water to a planet to grow crops on it
Applying fertiliser will speed up the process
3. Trade
You can sell crops and buy water/seeds/fertiliser on other planets to further produce more crops.
Right click on a building to open trading ui