Need to create an IAM User with access to S3 and AWS CLI

Hello.

AWS re:Post is a community forum site, you cannot sign in to your AWS account and create an IAM user.
You must create and configure IAM users yourself.

Create an IAM user using the steps in the document below.
At that time, please set the IAM policy necessary to access S3.
https://docs.aws.amazon.com/IAM/latest/UserGuide/id_users_create.html

After creating an IAM user, issue an access key using the steps in the document below.
https://docs.aws.amazon.com/IAM/latest/UserGuide/access-keys-admin-managed.html

Once the access key has been issued, please set the access key by following the steps in the document below.
https://docs.aws.amazon.com/cli/latest/userguide/cli-configure-files.html#cli-configure-files-methods

By the way, AmazonS3FullAccess is a powerful IAM policy, so if possible, I recommend creating an IAM policy that focuses only on the minimum necessary S3 actions.
Also, if you don't need long-term authentication information, I think it's a good idea to use IAM Identity Center, although additional settings are required.
https://docs.aws.amazon.com/singlesignon/latest/userguide/get-set-up-for-idc.html

If you just want to use the AWS CLI, there is also a way to use CloudShell without issuing an access key, so I recommend checking that out as well.