Creating databases and usernames, linking them to mysql

Hello I'm working through the 'ruby on rails 3 essential training' and am having an Issue understanding the theory behind what I'm doing. My issue is that even after granting permission to my databases/usernames I still cannot perform a db:schema:dump or run migrations.

From the command line, when I perform, mysql -u root -p I can see the databases I have and grant permission to the user.

After creating a new user called simple_cms, from the command line, when I perform: mysql -u simple_cms -p I can see the databases I have and grant permission to the new user.

My problem is when running migrations and trying to link my databases to the user I get, Access denied for user 'simple_cms'@'localhost' even though I have granted permission. At this point I'm confused at the difference between my new user (simple_cms) and user (root). Both have different databases so when trying to run migrations or schema:dumb, I'm not sure which one I'm accessing or why it is telling me that I'm denied access. I'm sorry if this is confusing, its equally frustrating, let me know if you have any suggestions or could explain the theory behind all of this. Thanks!