Hi JC,
If you are using single sign-on then you don't need to login multiple times. You have to login once and then you can access all the systems you are authorized to use. In your previous project they must be using single sign-on.
In case you are not using single sign-on you need to login separately for all the systems which you want to use/ authorized to use.
In store MIM is SAP portal for store personnel to perform the store operations eg. Raising Sales Orders.
Thanks,
Vikrant.