You are right you need to format it like var1=1&var2=2. The problem is it can be confusing mixing up & that means "add these strings together" and & which is part of an actual string.
"var1=" & user.texbox.Text & "var2=" & pass.textbox.Text
will result in a string like this:
Note the missing & because all your & mean "add strings".
This should fix it:
"var1=" & user.texbox.Text & "&var2=" & pass.textbox.Text
Note the & inside a string meaning it is literally included in the text rather than adding strings together.
Edit: just to clarify, don't use this for anything remotely serious! I know you know, but I just want to make sure I say it, because this is incredibly insecure :)