There are two places where you can now save content blocks from.
First, when you are creating a template with the template tool, you can hover over the content in question, then look for the 'save' icon, circled in red in this image:
You can then give the new "block" a Title, and select the type (Body, Listing, Article, RSVP). Then click Save Content.
You can also save content blocks by using our Dynamic Content Block Creator. To utilize this, click Marketing Materials > Manage Content Blocks.