To save and use your blocks or elements just follow these steps:
Press the 'save' button on the block or element you want save.
Enter the name you want to use for this block or element:
After naming your block, click on '+ block' in the upper right of the editor:
In the overview you will have the opportunity to select from the 'saved' tab. There you'll be able to view all of your saved blocks or elements when you select '+ element' in the previous step.