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