To use blocks in an existing site, first, enable the site edit mode from the menubar.
Then click the “Add a block” button to add a new block. Here, you will find Edmo’s custom blocks, and you can use any block that you want.
To edit the block click the settings icon and hit Configure (Block name) link
To make an image URL check this doc: How to use blocks in existing site?
With these guidelines in mind, you can efficiently use the power of blocks to improve the functionality and design of your site.