On MSSQL 2012 on Windows 7 (localhost)

Authentication, authorization, usernames, permissions, passwords. These things have been the bane of my professional career, as I have not yet had training to comprehend them, but in my career they have CONSTANTLY prevented me from progressing at certain tasks. So again, I am at that cross road.

I can create a database called 'test' while I am logged into the localhost server under a windows account. I notice there are 2 areas of 'security' (one under the database in the enterprise manager which I believe holds logins on the database in question and another under the server itself which I believe holds all logins respected at the server level)

When I expand the database security, I notice the following logins: dbo, guest, INFORMATION_SCHEMA and sys. Traditionally I would expand the security under the server itself, right click on the account I wanted to give access to the DB (in this case, it lists the same windows account I am logged into the server with) and under properties, I'd select USER MAPPING, and turn a tick on for the DB in question, setting the USER and DEFAULT SCHEMA fields to 'dbo'.

Well, for whatever reason, it's like that (and the role membership has PUBLIC and DB_OWNER on). Yet I cannot login to the database. Usually with at least SQL logins, the user you add here then appears under the Database's SECURITY folder, but I do not see my Windows Login listed there.

So I'm at a loss. Any clarification is appreciated. If someone knows of a great online resource that explains SQL server rights and logins, that would be fantastic.