The first post you need to read is Attributes and Equipment in Guild Wars 2. Tasha does an excellent job describing primary and secondary attributes and what they affect, how condition damage is calculated, what are the base health pools at level 80 and how to improve everything through armor and accessories. There is a lot of detail and information and I've found it to be a fantastic reference guide for helping my choose armor depending on what I'm looking for. in my build/play-style. And if that were not enough, she discusses back items (I didn't know we could have these!), crests, sigils, runes and aqua breathers.
Power vs Precision is the next post that is a must read. Do you want crit? Raw power? Which is better and how much do you need? Don't know, read the post. She calculates how power and precision affect damage for 1 hit and for 100 hits. She does the math so you don't have to.
Vitality vs Toughness - I cannot recommend this post enough. If you just want to read one, read this. I knew there was a difference between vitality, aka health, and toughness, which only reduces direct damage, but really didn't understand them until reading this post. Ultra condensed understanding - Vitality helps you avoid dying to conditions, toughness keeps you from getting crit'd to the ground. I still go back to this post as a refresher.
I highly recommend checking Tasha's page periodically. She produces excellent posts and information. You can find here page here http://www.tashadarke.co.uk/ or in the links section titled "Warband Board".
See you in Tyria!