1) To post HH on this forum you can either just straight up copy/paste it directly from the downloaded hand history text file, or you can use one of many hand converters out there that translate the text into easy to read formatted text, or even videos, including CardsChat's own Hand History Converter
! I personally use www.pokerhandreplays.com (http://www.pokerhandreplays.com) just because for some reason the CardsChat one goes all screwy on me sometimes (it's just me, or my computer, or my browser, so don't let it turn you off to a wonderful tool). They are usually pretty self explanatory, but let me know if you have any questions.
2) Once you've got your hand history, you can post at either:
Tournament Hand Analysis (http://www.cardschat.com/f51/), for all hands from STTs, MTTs and SnGs, or
Ring Game Hand Analysis (http://www.cardschat.com/f50/), for all hands from ring games, either full ring or 6max.
People usually appreciate some context about the hand (i.e. if you have any reads on your opponents, your own table image, what you think about the hand, etc.) in addition to the hand history itself (which can be posted directly as copied text, or as a direct link to the hand history itself).
Also, it is considered basic HH post etiquette to not reveal the result of the hand until you've gotten a few responses. All brag posts and bad-beat stories belong in the appropriately named Brags, Bad Beats and Vents (http://www.cardschat.com/f46/) forum. For the basic guidelines, visit the Tournament Hand guidelines (http://www.cardschat.com/f51/hand-analysis-posting-guidelines-68850/), or the Ring Game Hand guidelines (http://www.cardschat.com/f50/hand-analysis-posting-guidelines-87481/) for specifics.
3) I usually keep my hand histories for 30 days, although I've never really looked at anything more than a week old. I try to analyze my hands while the context surrounding my decisions is still fresh (i.e. was I on tilt, tired, nervous, in a hurry, cool and collected, on a bad run, on a rush, etc.)
Hope that helps! Cheers,