As the name suggests, Reusable Blocks are Blocks that you can re-use anywhere on your site. A Reusable block can be added to any Page or Post, and as many times as you want. If you update or change the style of your Reusable block, the changes are automatically applied to that block, right across your whole site.
To create a Reusable Block, simply add a block, add your content to the block then style it how you'd like it to appear. Once you've got the block looking how you want it, click the Add to Reusable Blocks option under the More options icon on the Block Toolbar. You're then prompted to enter a name for your Reusable Block. After doing so, click the Save button to save it. Your new Reusable Block will appear under the Reusable tab within the Block Inserter.
If you’d like to remove or edit any of your Reusable Blocks, you can also click on the Manage All Reusable Blocks options under the More tools & options icon at the top-right of the page, or the Manage All Reusable Blocks link underneath your list of reusable blocks in the Reusable tab within the Block Inserter. Once you click this option, you’re presented with a list of all your existing Reusable Blocks which you can then edit or delete. Before clicking the Manage All Reusable Blocks option, ensure that you save your current Page or Post to avoid losing your recent changes.