Asp.net how to make Video Gallery like youtube

There is already software available for that; some with source code and some without. I don't know what they are but it is worthwhile to search for it.

If you must develop something entirely yourself, then you need to start by defining what you need. You can't develop something simply by deciding to create something like something else; you must describe what it does. For example, you need to have a way to upload files and with descriptions and a way to search the descriptions. You need a way to create small images that represent what is in the video. You need a way to present the videos in various formats. Most of that would be done by photo viewing sites, not just video. So you can look for code that manages photos and that could be easily converted to manage videos. You will also want a way to manage memberships. All of this are separate tasks and you should ask one or more questions about each one. You must however do some reading and researching yourself first.

There are many useful articles and even books in this web site. Start b y looking at those.