Display user name when logged in

Yes. as Raja said. use static variable and assign login userid to variable then you can access them everywhere in project.
static variable act's like a global variable. you can use public module with variable used as Global.

Create global variable in VB.NET windows application[^]

and Take label on each form to assign this variable.

It is very simple

here is the sample

Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
       Label1.Text = Form1.TextBox1.Text
   End Sub