Custom URL is the web address, which your fans or customer can easily remember and can enter directly to address bar such as youtube.com/yourchannelname. But Youtube has set some eligibility criteria for creating custom URL. Once you meet that criteria you can create a custom URL based on things like your display name, your YouTube channel name based on the availability. You can’t change a custom URL after creation. However, you can remove the custom URL from your channel and claim a new one if you want to change it.
General requirement for creating custom URL.
- Have 100 or more subscribers
- Be at least 30 days old
- Have an uploaded photo as channel icon
- Have uploaded channel art.
To learn more about creating custom URL and setting custom URL check the below link.