A Twitter Ads account is how you can set up, run, and analyze Promoted Tweet campaigns on Twitter. You must sign up for a Twitter Ads account at ads.twitter.com, after which you'll have a Twitter Ads account in addition to your organic account.
Your Twitter Ads account is linked to the handle you create it from. For example, if you have a personal Twitter account and a business Twitter account, log in to your business Twitter account and go to ads.twitter.com. From there, you can sign up for Twitter Ads and promote content on behalf of your business Twitter. Ads will show up as being "Promoted" from the handle of your Twitter Ads account.
Keep in mind there is no difference in the account creation process for Twitter accounts for personal use and Twitter accounts for business use. The difference is how you decide to use your Twitter account.
Learn more about creating a new Twitter account.