k where do i put it? just in the folder with my site?
The root folder (where your index.htm file is)
You may want to add this to the Meta area of your index.htm file...
<meta name="revisit-after" content="15 days">
<meta name="ROBOTS" content="INDEX, ALL">
<meta name="ROBOTS" content="INDEX, FOLLOW">
This tells robots that your site can be indexed.
BTW: My robots.txt file only blocks some of the YaBB files, which, quite frankly, isn't a really good idea... if you have a forum, you will want to block the admin directories and the member directories. This will keep important information about your users from being searched if the search engines manage to do that.