I committed to 'TeX, LaTeX and Friends', so could anyone point me how to fulfill that?
If you go over to http://area51.stackexchange.com/, click on one of the proposals in commitment stage, and click on commit, it says:
I commit to participate actively in [site] for at least three months, especially during the private beta, and to ask or answer at least ten questions.
This answer on meta.SO says you need 10 posts (questions or answers or a mix). I don't think they need to be in the private beta, you could start posting now
I think the commitment was for the private beta, and you missed that by a week. However I don't think stackexchange will come and arrest you because of that ;). So if you want to see this site flourish, just actively use it now and in the coming months of public beta (and if every thing works alright on the finial site after the beta).
You missed a badge, and opportunity to "reclaim" commitment to commit to another area51 site. You need to wait until end of public beta now for the "reclaim".