How do I add columns in WordPress?

You can add columns by selecting Add Block > Design > Column:

columns block

Then, you chose a layout. If you choose Skip, you will get the first option of two equal columns:

columns ratios options

Now there are two equal sized blocks that you can add content to. Add a block type by clicking on the plus sign, Add Block:

add blocks to columns

You can find more information regarding adding columns using WordPress at: Columns Block – WordPress.org Forums