The selectors are entirely individual to each website/application. It all depends on how the site/app was built, since the robot are just reading CSS & HTML items as “selectors” to use.
If you are having trouble with it, you can show us a screenshot of the element you want displayed in uiexplorer - make sure the whole tree on the left and in the middle is displayed for us to attempt to help finding a suitable selector. If it’s a publicly available site, then a link would be much better though