Crafting focus is like a special buff you can activate to receive a higher % of raw material back when refining.
Lets say you refine100 raw wood, without the focus you would get 100 refined wood + 15 raw wood (15 raw wood is the return).
Now if you use the crafting focus points, you would refine 100 raw wood + 100 focus points, and get 100 refined wood + 50 raw wood (50 raw wood return).
This focus points are really useful when refining rare resources, like a 5.4 for example. This way you can use the returned materials to refine even more.
Now these numbers I used are probably wrong, cuz I dont remember the % that is returned when using focus.
A certain Amount of focus is gained every day if your account has the premiun status.