Well, you might think it's easy but not everyone will think like you and it's not as easy you might think.
There are two things here one is the channel name (can be changed at any time) another thing is the actual username which (username) can never be changed even though you get millions of subscribers.You can find the username at the end of the URL like this https://www.youtube.com/user/AreWeFamousNow
Let me tell you why I chose this URL, because when I searched Karim on youtube it showed karim's two channels KARIM and KUKU that's because these two channels are related so the search engine showed these two first and some channls and videos too.
But those two are just names of the channels not the usernames and actual username of KARIM is AreWeFamousNow and the actual username KUKU is TeamKuKuTV and full URLs are
Where can you find the URL?
You will find the url by going to the main channel page and then in the address bar at top.
Another way of finding out the username by moving your cursor over the channel name (which you will find under every video title) and the url will appear at the bottom like the picture below.
Well, that's all for this post I hope you liked. Thanks