In order to add a block, click on the Add Block icon:
Still it’s up to you which of the essential blocks offered you want to see on your site and which you can skip.
Click on the block itself to add it on the site:
You can also copy an already existing block. For that, click on the three dots in the top right corner of the block and click Duplicate (will add a block right after the previous one) or Copy to…(will copy the block to another page).