CINELERRA-GG is a complex and feature-rich program. Using a guide is indispensable. The official manual (in English) can be found in PDF and HTML format:
From within the program, you can invoke Context Help, which references sections of the HTML manual1.
Context help can be requested from almost any CINELERRA-GG window or subwindow by pointing with the mouse cursor on the GUI element of interest and pressing Alt/h. That HTML manual page will be shown via the configured web browser, which is assumed as most relevant to the GUI element currently under the mouse pointer.