How do I create a Unity account for the Acquire dashboard?

All users require a personal Unity ID account, which you can create here:
https://id.unity.com/account/new

Then, you can create an organization to hold your projects. You can add a single user account to multiple organizations, all containing different projects. Check this article for more information:
https://support.unity.com/hc/en-us/articles/208592876-How-do-I-create-a-new-Organization- 

Once created, you can set up your advertiser account on the Acquire section by adding an app.