First off, welcome to Android Forums!
First you will want to connect your phone to your computer via the micro usb port on your phone that is also used for charging.
Once connected (if using windows):
go to "my computer" and look for your device should show up as "removable device"
if this is a video you recorded
go to :
- DCIM
then go to: - Camera
from there you can just drag and drop to your desktop or where ever you would like to store the video.
If it is a saved video look in the downloads folder, or media folder.
I unfortunately not answer it if you are not using windows as I do not have much knowledge on other OS. If this does not answer your question, try resubmitting it including your computer operating system as well what kind of phone you are using.
Thank you for your question! Have a great day!