Open settings (gear icon on left). Then choose Editor on left and scroll to see and enable Fold heading and Fold indent.
In your image, the triangles are heading folds.
Fold indents applies to lists and even as little as a single space of indentation, but I usually use tabs to keep it consistent and a little more obvious.
To start a list, you can do - then a space. You can also use a single asterisk then a space, but you should be aware that with two asterisks, anything between them is bolded, so avoid that. This previews as a circle bullet. You can also initiate a checkbox list with a ctrl enter. Another ctrl enter will check the box, and again will uncheck it.
Hope that helps some. The search function and quality of posts here on this forum is great if you are patient. The help (?) icon above settings gear opens the help vault which demonstrates a lot of functionality. Using the split and linked panes and having one in edit and other in preview is great to quickly see what’s available and how it is accomplished.
Good luck.
