How do I change the default way that the contents of a folder are displayed?

What do you mean "by symbols"? Do you mean the folder is displayed in Icon View?

By the way, this has nothing to do with being in the Sidebar or not - the way a folder is displayed is determined by the View options.

If you want a folder to always appear in List View: with that folder open, press Command-2 to switch to List View; press Command-J to open the View Options; check the box at the top "always open in List View".

Nurv288 wrote:

I guess I mean Icon View? I'm using a Mac in a different language.

I assume "Use as standard" makes it so every folder always open in List View. Am I correct?

Not exactly,. All folders that you have never opened and set the view should open in that view.