You can't really make youtube.com/user/username URL's anymore...At least not that I know of (Youtube calls them Legacy usernames now). They might be adding this feature back once they get rid of google plus this year.
What you can do is get a Google Plus URL so like google.com/+GeneralComedy would get you the URL youtube.com/generalcomedy to whatever youtube it is connected to, in this case
https://www.youtube.com/user/Twsmith24
You can swap google plus pages between youtube channels, so basically if you have an OG google plus name then it is a transferable youtube username.
Hope that helped fam ;P