How to enabled and disabled login and log out button

Hello

I have Query 

I am designing new website 

I want to know how I came to knoe whether user is logged in or not 

so that i can make visible log out button on MAster PAge 

 I am able to log in but my log out button is not visible since after successfully login i am getting log in button visible 

can you please let me know where I am wrong ? 

and How to store value in session ("UI")  ? 

  Protected Sub Page_Load(sender As Object, e As System.EventArgs) Handles Me.Load
        
        If Not Session("UI") Is Nothing Then
             Logoutbutton.Visible = True
            LoginButton.Visible = False
            Displayprofile.Visible = True
            Displayprofile.Text = "USER profile"

        Else
            Alert.Show("no session")
            LoginButton.Visible = True
            Displayprofile.Visible = False
        End If
end Sub