Hi Alex Koshel,
As per my understanding from screenshot, you have used website option while setup your website(Kentico 11 provides two development ways 1. Web Application 2. Website while setup Kentico website). As per Kentico11 Documentation, If your web part consists of multiple files (such as other ASCX controls, images, JS scripts), place these files in a sub‑folder under the directory containing the main web part's files.
So if you want call your RadwareClossaryPageType class file then place into \App_Code with create folder i.e. your sitecode name and place your class.
\App_Code[Folder with your SiteodeName]\RadwareClossaryPageType.cs
Directly you can call your class on your webpart page like below -
RadwareClossaryPageType radwareproperties= new RadwareClossaryPageType();
For better understanding about export folder structure refer this - https://docs.xperience.io/k11/deploying-websites/exporting-and-importing-sites/export-folder-structure