Hello, I'm a beginner in Magento.
I have a question about editing the sidebar.
I'm looking for how to edit the red circle section in the picture above.
I checked csm static blocks but there was nothing except footer.
Anyone can help?
It looks like you've bought a theme for Magento, so it's customized solution. Further, that sidebar is called "layered navigation," and in general, there is no easy way to manipulate with it. It's generated from a couple of PHP classes and phtml templates which serve for rendering the different type of attributes (category, price...).
Those "files" affects layered navigation in Vanilla Magento:
Since you're probably using customized solution, it may differ for you.