An IAM user is a user that has a limited number of rights to the systems and resources that AWS has to offer. Since there are so very many resources available and so many actions that you can perform on those resources, setting up an IAM user with just the right permissions can be tricky.
For Audit Trail Cloud, we have gone through the process on your behalf in order to make some of the work easier.
In order to create a user, you will need to have the right permissions yourself. Either you log in as the root user or as a user that has full IAM permissions.