If you have signed-up for Google+ or any of the Google products, then you have also created a Google Account. Once logged in to YouTube with your Google Account, you can like videos, subscribe to channels, and flag videos using just your Google Account. You can also add videos to Watch Later.

However, in order to perform certain actions on YouTube (such as uploading, commenting, subscribing channels or creating playlists), you'll need to create a YouTube Channel. If a Google+ profile exists on your Google Account, you have the option of using your Google+ name and avatar as your YouTube identity for your new Channel. For more information on YouTube and Google+, please view this guide.

Note:- This is for new Channels only. If you have an existing Channel, Google doesn’t currently support Google+ profile integration.

To create a new Channel with a YouTube username instead, Google+ users can select the Create a username option.

Q.(i). How to change Google+ identity on YouTube? Or, How can I create a YouTube Username?

A. Please follow the steps below to change your Google+ identity on YouTube.
       1. Click on your name at upper right of the page.
       2. Click on "YouTube Settings"

           3. Overview
           4. Click on "Advanced" next to your profile image 

           5. Click on "Create username"(Create a username for this channel and hide the Google Profile information associated with it.)

           6. Give a name of your channel and check " I understand that my channel will be renamed."

           7. Click on "Create Username" > Save.

Q.(ii). Can I change which Google+ profile I use with YouTube?

A. Once you create a Channel with your Google+ identity, your YouTube Channel is tied to the Google+ data of that particular profile. There’s currently no option that allows you to switch the associated profile and/or Google Account that you use on YouTube.

If you created a Channel using your Google+ identity and would like to switch to a username, please take a look at Q.(i).

If you’ve accidentally created a Channel with a Google+ profile or Google Account that you did not intend to use, you can delete the Channel. Check the Deleting your data section for more information.

Q.(iii). What happens to YouTube if I delete my Google Account or Google+?

A. If you delete the Google Account to which your YouTube account is linked, you will delete both the Google Account AND your YouTube account, including all videos and account data.

If you are using your Google+ identity on YouTube, and you delete your Google+ profile, you will also delete your YouTube account, including all videos and account data. If you don't want to delete your YouTube data, you can create a YouTube username. Please see Q.(i).

Please see the details here.

Note:- Once you’ve created a YouTube Channel with Google+ integration, the following is true:

• You’ll use your first and last name from Google+ as your YouTube identity
• You’ll use your Google+ avatar as your YouTube avatar
• Your Channel title will use your Google+ identity. So if your name on Google+ is John Smith, your Channel’s title becomes “John Smith’s channel”

Request:- Please post your YouTube related query on YouTube Product Forum.