difficulty with "for" loop

Hello. I'm learning about for loops. The first example below I understand but I'm confused about the second. Is it just incrementing throug the code? If so, could you just put "imynumber2" without the +1 after it?

Sub OurFor()
Dim iMyNumber as Integer

    For  iMyNumber= 1 To 100
    iMyNumber
    Next iMyNumber
End Sub 

Dim iMyNumber as Integer
Dim iMyNumber2 ad Integer

    For iMyNumber= 1 To 100
    iMyNumber2 =1+iMyNumber2
    Next iMyNumber

End Sub