"Transgender" is a pretty broad umbrella. Just about everyone here is either transgender, or is wondering whether they might be transgender, or is the spouse of someone who is.
"Transsexual" implies that they are pursuing modifying their body with hormones and/or surgery, or have already done so.
The definitions don't limit where you can post. If you have something to say or ask relating to the subject matter of the forum, go right ahead.