How do I render videos in iMovie

If you are using iMovie 10.2.4, and it crashes when you try to export a movie then that likely is caused by a bug that has been reported several times on this forum. Until Apple fixes it, the solution is to go to System Preferences/Language and Region, and set the region to United States and the language to English.

-- Rich

I don’t know what you mean by “sometimes goes blank”.

To export a project, click on the export button (the square with the upward pointing arrow in it) located in the upper right of the project screen and, from the export box that appears, click on the File option. Other dialogue boxes will pop up where you can select your settings and destination. That will create a standalone movie that will play anywhere.

— Rich