When you set up your ads account, your handle will become an account administrator by default. This is the highest level of ads account access. As a result, you can grant varying degrees of access to other Twitter users.
You must be logged into an account administrator handle in order to grant other users access to the ads account.
There are five levels of access that you can grant to other users, each with a different set of permissions. Which level you grant depends on what you want the other users to be able to do within your ads account.
You grant access to others by adding their handle and choosing what level of access you want to give them.
From there, when that user is logged into their handle, they can go to ads.twitter.com, enter your ads account, and perform the actions permitted to the access level you granted them.