How to create a separate YouTube channel under the same YouTube account?

If you are asking: "Can I create a separate YouTube Channel other than the main YouTube Account?", then the answer is "yes". When we sign up for YouTube Account, we have to create a Google Account. If we already have a Google Account, we just have to sign in with the same Google Account.  YouTube account is not the YouTube Channel, that is, YouTube Account and Channel are different things. Google Support says:

"With a Google Account, you can watch, like, and subscribe. Google Accounts don't come with a YouTube channel by default; without a channel, you have no public presence on YouTube.

To upload, comment, or make playlists, create a public YouTube channel. Currently this can't be done in the Android or iOS YouTube apps, but you can use the mobile site or a computer:"

The above information about YouTube Channel from Google Support is pretty clear. We can watch, like and subscribe but cannot comment, make playlists and upload without a YouTube Channel.

First of all, how to create a YouTube account?

1. Open your web browser and go to YouTube.com.
2. Click the “Sign In” button located at the top right corner of the page.
1. If you already have a Google Account, sign in with the same Google Account.
3. Else, if you do not have a Google account or want to create a separate Google account, then click “Create Account”.
4. Fill out the registration form on the right.
5. Agree to Google’s terms of service and privacy policy.
6. Click “Next Step”.
7. Add a photo and then create your new profile.

Till here, we have signed up on YouTube with the existing Google Account or new Google account created. We can watch, like and subscribe. But we cannot comment, create playlists or upload videos. We need to create a YouTube channel.

A) Create a personal channel with your name

1. Make sure you're signed in to YouTube. 
2. Try any action that requires a channel: e.g. upload, post a comment, or create a playlist.
3. If you don't have a channel yet, you'll see a prompt to create a channel.
4. Check the details (with your Google account name and photo) and confirm to create your new channel.

B) Create a channel with a business or other name

• On a computer or in a mobile browser, make sure you're signed in to YouTube.
• Go to All my channels. (URL = https://www.youtube.com/channel_switcher)

• Provide a YouTube Channel name, select the category and agree to the terms.
• The YouTube Channel comes with a Google+ Page.

After creating the new YouTube Channel, we can switch between the YouTube Channels from the account icon on the top right hand-side corner. We can then manage the accounts separately, and upload videos in the respective channels.