https://docs.magento.com/m2/ce/user_guide/cms/block-add.html

Adding New Blocks

Custom blocks of content can be added to any page, group of pages, or even to another block. You can place code for a carousel image slider in a block, and then position the block on the home page.

The Blocks workspace uses the same basic controls as the Pages workspace to help you find blocks and perform routine maintenance operations.


Blocks Workspace

To create a block:

1. On the Admin sidebar, tap Content. Then under Elements, choose Blocks.
2. In the upper-right corner, tap Add New Block. Then, do the following:

New Block
a. By default the status of the new block is enabled. If you want to change the status, set Enable Blockto “No.”
b. Assign a Block Title for internal reference.
c. Assign a unique Identifier for the block. Use all lowercase characters, with underscores instead of spaces.
d. Select each Store View where the block is to be available.
e. Complete the block Content as needed.
  • Use the editor to format text, create links and tables, images, video, and audio.
  • If you prefer to work with the  HTML code, tap Show / Hide Editor.
3. When complete, tap Save Block.

The new block appears at the bottom of the list in the Blocks grid.