Q:

Next cell when button is clicked

Below the code.  It currently just gives the first cell out and i don't know why it doesn't go to the next cell, when clicking on the button. 
Private Sub CommandButton3_Click()

 Dim notFirst As Boolean
 Dim rng As Range

 If notFirst Then
    If rng. Row = 104 Then
        Exit Sub
    Else
        Set rng = rng. Offset(1)
    End If
 Else
    Set rng = Range("A102")
    notFirst = True
 End If

 Range("C8").Value = rng. Value

End Sub

How it looks like:
https://www.bilder-upload.eu/bild-73e0c4-1584092523.png.html
https://www.bilder-upload.eu/bild-5cfb6a-1584092581.png.html

A:

This might work for you:
Public notFirst As Boolean
Public rng As Range

Private Sub CommandButton3_Click()

 If notFirst Then
    If rng. Row = 104 Then
        Exit Sub
    Else
        Set rng = rng. Offset(1)
    End If
 Else
    Set rng = Range("A102")
    notFirst = True
 End If

 Range("C8").Value = rng. Value

End Sub

These Public variables make sure that when you click your button again the last assigned value is still present.  Note that I would not nesecarily recommend the above code to do what it is you are doing.