new to rails, setting up db then running rake db:create/migrate

You run rake db:create once and only once, and you run it first. Then you run rake db:migrate every time you add/change a migration. You've either already run this migration, or you are pointing at a database that already exists and already contains a table named users. My guess is that you ran the migration once already, in which case you're probably good to go. If you want to nuke the DB and start over, do rake db:drop db:create db:migrate.

We can simply give, it will do all the rake task which is require for database creation and migration

rake db:setup