You can add a new user by clicking on Users → Add User. In that screen you can define their Name, Email address, as well as the privileges they have in Paymo. After you click Save User, they will be notified by email and will be able to set their own password and login.
Alternatively you can invite a user when you create a project, from the “Assigned Users” section. When you create a new project you can either assign existing users or invite and assign new users.
Note: During the 15-day trial period you can add users with no restrictions, but after the trial period expires you can’t add a new user if the subscription doesn’t allow you. For example if you’ve subscribed for 10 users and you already have 10 active users, in order to add one more user you either archive an existing active user or modify your subscription to allow 11 active users in your account. When this happens you will be redirected to Subscription and billing section in order to change it.