Show item in sidebar only on blog view or blog post?

I tried to search for this, but came up with so many other topics (the search terms are so generic), I had to post. Sorry if this has been covered.

I want to show an item in my sidebar ONLY when I am viewing my blog page or a single blog post (my site consists mostly of Pages, but has a blog section that I want to customize the sidebar for). What do I use?

Here’s my site:
http://weheartgames.com

Thanks!
-Mike Berg