So that only your title will show in the dashboard rather than the entirety of the content?
I had the same question when I first started. The quick answer is, you can't, not in the usual way. Click on any of my posts and you'll see the solution I came up with -- I create an ALL CAPS title at the top and assign it an H2 treatment then skip a line and compose the body of the post.
Seems to work okay within the formatting limits of these boards.