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Edit the page to which you want to add a block. The toolbar at the top left of the page contains six buttons. The leftmost button, Add Block (blue square with a plus sign inside), is for adding the different types of blocks to a page:
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After clicking on Add Block, a list of blocks pops up. You can search for block types (see Table below) using the search bar, type “/t” to bring up blocks that begin with the letter T, or click through various categories to find a block type:
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After clicking on “Table”, you will get the image below on the page and then you can pick the desired column and row count:
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A full list of blocks can be found at this Wordpress Support Page.