Instructions to add another AWS account/user to my AWS account

Here is a great step by step video showing "How do I set up an IAM user and sign in to the AWS Management Console using IAM credentials?"

https://www.youtube.com/watch?v=wRzzBb18qUw

And a knowledge-center article as well

https://aws.amazon.com/premiumsupport/knowledge-center/create-new-iam-user/

Is this what you are looking for - https://docs.aws.amazon.com/IAM/latest/UserGuide/id_users_create.html