This is a single step process if you have already downloaded and installed AWS CLI. If not installed, check out this link and install the CLI according to your OS.
After installing it, type in this command - aws configure
This command will ask you for the access key, secret access key, default region. So, provide these details and hit Enter to save them.
Once that is done, you are pretty much set. Now, it is just one command to create a bucket. Below is the command:
aws s3 mb s3://bucket-name-here
Make sure the bucket name is unique, else your command will fail.
This is the output you will get if the command is successful:
Hope this helps you!