You do that by putting 4 tildes, as EmpyrealInvective has told you twice. When you press publish, that will convert into a link to your talk page, as if by magic. You can do it in the forums even. Try following the advice that's been given, and add this at the end of your next post here:
When you press "Reply", that will convert into the link and date. It's really that simple.
Another way to put a link to your profile would be to look for the options for the font like slant or bold and right next to them is an animated chain. push that, and type in what you want it to show up as, then put the link to your profile.