You go to the pattern library, copy a pattern and paste it into your editor. I did that here and replace the 3 images that it came with. I added some captions. Using this pattern.
Here is another pattern.
And the days are not full enough.
And the nights are not full enough
And life slips by like a field mouse
Not shaking the grass
– Ezra Pound
I don’t think I am quite ready for the Block Editor yet but these look interesting.