The most obvious suggestion is the best here, pick it up and read it start to finish. It shouldn't take too long, as there is a lot of stuff you can skip upon first reading (Background, technical stats) which you will only need later. Then once you've done that you'll have a good idea as to how your army's codex is laid out, so you know where to look for information when you need it.
Read your codex
Read the codex
Read the codex
Read the codex
Read the codex
As in purchase? look at the Gamesworkshop website. Play with? read the codex.
1. Red Dragon Codex 2. Bronze Dragon Codex 3. Black Dragon Codex 4. Brass Dragon Codex 5. Green Dragon Codex 6. Silver Dragon Codex 7. White Dragon Codex 8. Gold Dragon Codex 9. Blue Dragon Codex 10. Copper Dragon Codex (2011)
it varies based on what you arm it with. Read the ork codex for an exact amount
The Codex was created in 2005.
Get a Codex and read it. If you don't have 2 troops and an HQ you can't play anyways.
The next 40k codex in line is the Blood Angels codex.
The Codex was invented in the "Ancient Times"