The 3 "aptitude" tests (i.e. basic checking, spatial/cubes, and the diagramming/code) are done individually with a separate time limit each. So basically, when it comes to that part of the day, you go into the room, there are 3 booklets on the table, and the person in charge will stand up at the front, tell you what book to open, what paper to use, explain everything, go through a mini practice and then start the clock. They will tell you when to stop, and then you open the next test booklet, they tell you what to do, practice....and so on.
You will be told when to do everything and where and how to do it. So no need to worry. They guide you through it all like you were back in primary school. The only thing they won't do is tell you the answers in the proper test!
As for the diagramming, I believe the commands were the same as in the practice tests you get emailed, or can find on the website. Although, I think in the proper test, there were a few extras thrown in. No need to fill your head with the commands before you go - there's a little flip out "code card" to keep beside you when you do the test.