If you are going to have a universal log in username and password, you can use the following code:
If txtUsername.Text = "Your Username" & txtPass.Text = "Your Pass" Then
If you are checking usernames and passwords from a SQL Database or using there log in information from your website to sign into the application, then that is a different story. I have created a log in form form my webs.com site so I could help you if you don't know how to use or create a SQL database. If you are using a database then I can not help seeing as how I have never dealt with a databse. I am a self-taught coder so I am not the best by any means.