database and authorization

i know the basics about how to manipulate SQL server database, i mean the code itself, but there are few other things which i don't understand.

first, databases which i have created by my own, i can use only when
i have the website itself open (i get an icon at the taskbar)
but database such as 'master' which came with the sqlserver, i can acess always even without running the page with visual studio first. i have no idea why.

also, when i try to connect my website using my ip, i can only do it with
the master database.. those i created by my own i can only connect when i enter the URL page as localhost.

I don't understand what's USER INSTANCE for and how do i really set
a database username and password

can someone exaplin a little? thanks, because i am very confused .from the post it is not clear what your problem is. do u mean that u can connect to master database but not to the one u created? please ready the Sticky post at the top to make a more meaningful post if u are interested in getting proper reply....|||Hi

Are you using Visual Studio to look at your database, or SQL Server Management Studio? The second one is the preferred tool. The first is something you are more likely to use if you are a webby developer rather than a database developer.|||I have them both.
I'll try making it clearer, a question in each reply.

I have for example 2 databases, "phynew" which i created and "master"
which comes with sql server.

when i am using the master database i can always connect
whether i type
http://localhost/Learning/Default.aspx
or with ip
http://82.81.184.139/Learning/Default.aspx

but when i am trying to connect "phynew" i need to use the debugger so it will give me a port
i need to type the port in the URL (automatically done when i use the debugger) or else i get a connecting error.
http://localhost:4606/Learning/Default.aspx
when i type
http://82.81.184.139:4606/Learning/Default.aspx
the website doesn't work at all.

therefore i can't give someone else a working URL if i am using own created database.
what's the difference between those databases?