Spam blocker?

Give this a read, it may help you out.

http://codex.ww.wp.xz.cn/Combating_Comment_Spam

Is there a plugin I can install to block spam for me?

There are lots of plugins you can try.

http://ww.wp.xz.cn/plugins/search.php?q=spam

These two combined are pretty effective.

http://ww.wp.xz.cn/plugins/akismet/
http://ww.wp.xz.cn/plugins/cookies-for-comments/

I’m also fond of this one.

http://ww.wp.xz.cn/plugins/spam-destroyer/

Give those a try, they should help you get the spam problem under control.