Edit post theme format – twentyeleven

I am trying to edit the format of the posts that appear in the category section. I am wondering if it is possible to only show part (if any) of the post instead of the entire post?

I like the default theme (Post title and then the full post), as well as the Gallery theme (Post title and then a condensed version of the full post) – however wondering if it is possible to either:
1 – Only show the post title and none of the post, or
2 – Only show the first sentence or first x% of the post.

Referring to #1 above, I have tried to insert the following:

.entry-content{display:none;
}

Into my child style.css, which gives me the effect that I am looking for; however, now when viewing the actual post the entry-content is also not displayed. Is it possible to only remove the display in the category section and not on the actual post?

Thanks in advance,