From the main menu, select Edit | Find | Find in Files Ctrl+Shift+F.

In the search field, type your search string. Alternatively, in the editor, highlight the string you want to find and press Ctrl+Shift+F. IntelliJ IDEA places the highlighted string into the search field.

To see a list of your previous searches, press Alt+Down.

If you need, specify the additional options.

IntelliJ IDEA lists the search strings and the files that contain them. If the search string is found several times on the same line of code, IntelliJ IDEA merges the results in one line.

To do a multi-line search, click the icon to enter a new line, and press Ctrl+Alt+Down/Ctrl+Alt+Up to browse through occurrences.

Check the results in the preview area of the dialog where you can replace the search string or select another string, press Ctrl+Shift+F again and start a new search.

To see the list of occurrences in a separate tool window, click Open in Find Window. Use this window and its options to group the results, preview them, and work with them further.

If you want to see each new search result in a separate tab in the Find tool window, click on the bottom of the Find in Files dialog and select the Open Results in New Tab checkbox.