The WordPress Block Editor offers a simple way to transform a block into a different type of block.
Clicking on the block icon in the top left of the block control bar, you are offered a list of options. This is the set of blocks which are available possibilities for transforming the current block.
Transforming a block is a useful and simple method for formatting your content. One click can change a short paragraph into a heading, or a longer paragraph into a list, for example, giving more structure and interest to your page.
Particularly useful are the options to transform a block into a Group or Columns block. This actually wraps your paragraph, image, video, etc within a new Group or Column block, giving you a quick starting point for managing the layout of your page or post.
Use Transform as a Shortcut for Wrapping a Block in a Group
Transforming a block into a Group or Column block is the equivalent of:-
- clicking the plus
to add a new block - finding and selecting the Group or Columns block, from within the Design category
- returning to your original block and dragging it inside the new Group or Columns block
to add a new blockUsing the Transform option just provides a nice shortcut and you can then go on to make the desired layout changes offered by the Group or Column block.
Transforming a block into Group or Columns actually wraps that block within a Group or Column, retaining the existing paragraph, image or video block
I find myself frequently transforming blocks into Group blocks, to enhance the layout by managing width, containing left- or right-aligned content, or adding additional spacing and margins.
Navigating the Editor
When your page contains a few more sophisticated blocks, such as Group blocks with nested blocks inside, it can sometimes be a little tricky to find and select the exact block you want to edit. The document list view provides an easy way to navigate within the editor.
Just click on the document overview icon 
in the top menu bar.
The document list view provides an easy way to view all of the blocks currently in your document and easily select a specific block, whether that is one of the containing blocks, or a block nested inside.
Click the same icon or the close button (x) to hide this window when you no longer need it.
Conclusion
Using the Transform option provides a nice shortcut when you realise that you need to wrap your content in a Group or Columns block. Groups and Columns can provide ways of producing interesting and beautiful layouts with the WordPress Block Editor.
For our introduction to the block editor, see Beginning with the Block Editor and Block Editor – Text and Formatting.