Once you are happy with your sequence, make sure to save and backup your project.
In your timeline window, select all of your audio/video tracks. Then set In (I) and Out (O) points before & after you first & last frame.
With the timeline window still selected, navigate to File > Output > Export to File…
Select the "Options..." button.
Set export as to "QuickTime Movie" unless otherwise instructed.
Select "Custom" instead of "Same as Source"and click “Format Options.”
Select "Settings..." in the pop-up that appears.
Set your compression type. If you have questions about which codec you should use, take a look at this article.
Select "OK" twice.
Make sure that "Video and Audio" is selected.
Under the Video Format tab, match the width and height to your desired export resolution (1920x1080 in most cases).
Select "Save".
Navigate to where you would like to export your project to, give it a name, and select "Save" again. Depending on the size of your project and the settings you chose, this may take some time.