A login ID is also known as a principal in SQlsever.

loginID = Similar to a ID that you would use to enter a building.

There are 2 types.

1.) logins created using mixed authentication

2.) logins created using the WINDOWS user ID

Lets talk about #1

Each new user who wants to do anything with SQl server will be given

a LoginID and a password to enter the database.

Now #2 - Similar to #1 except for the fact that SQL server will use

your WindowsID and password to enter you in to the database.

Usually when using #2 users will enter a user id that has 2 parts.

It will look like Andromeda\Brian_Hippo

Here, the name Andromeda is the domain name and Brian_Hippo is the actual userid used to login to the WINDOWS network.

I will leave the rest for someone else to answer. I could! But not the best answer.