The answer Optodata gave was a very good start already. Given that you repeat the question now, makes me understand that you are still struggling?
Also suggest to use the search function in this forum as most of the questions have already excellently been answered by the experts😊
Depending on the quality of your source material, and the required quality on Youtube, I would recommend that you use high quality if you have it. So if you produce the clip first and want to upload it separately go for 16:9 ratio, H.264 AVC MP4 is not a bad option (e.g. it works for me all the time), and select a profile like: 1920x1080, 24p pr 25p or 50p with 16Mbps (or higher depending on the nature of your video, e.g. more and faster movements might ask for higher bps).