Dig in. Q&A for asking specific tech questions.
Discussions for DISCUSSING tech topics, not asking for specific answers to technical questions.
Discussions > Water Cooler - Off topic forum for discussing anything but technical questions, work or anything relevant to IT.
That's it in a nutshell.
ie:
Want to know how to get rid of sirefef virus? Post in Q&A.
Want to discuss viruses and security ideas? Post to Discussions>Security
Want to discuss your favorite music, a band you saw on Saturday or whether or not evolution is a lie? Discussions >Water Cooler/Off Topic
The rest is just learning to type and click the mouse.
Oh yeah, you can find whitepapers and stuff here too if you want.