VBA: insert a variable number of rows - excel

Question

I've written the code below but I can't get past a line where I want to insert a variable number of rows. The compiler screams that it needs a "list separator or )" where there is a colon. But I can't find other ways of writing this. Please, help! =)
So, the problematic line is denoted by two stars from each end. Just above it there is a commented line that I've also tried with no success.
Also, would you be so kind and explain me what I need the following commands for (they are also found in the problematic line):Shift:=xlDown, CopyOrigin:=xlFormatFromLeftOrAbove
Finally, any suggestions of how I could improve the code, s.t., experienced programmers don't faint when they read it? =)
Huge thank you in advance,
Option Explicit
Dim ws As Worksheet
Dim Blatt1, Blatt2 As String
Dim Anfangsjahr1, Anfangsjahr2 As Integer
Dim reporting_Jahr1, reporting_Jahr2 As String
Public Sub Dreiecke()
For Each ws In Worksheets
If ws.Name Like "RVA_H*" Then
If IsEmpty(Blatt1) = False Then
Blatt2 = ws.Name
Anfangsjahr2 = ws.Range("A3").Value
reporting_Jahr2 = ws.Range("A1").Value
Else
Blatt1 = ws.Name
Anfangsjahr1 = ws.Cells(3, 1).Value
reporting_Jahr1 = ws.Cells(1, 1).Value
GoTo X
End If
Else: GoTo X
End If
If reporting_Jahr1 <> reporting_Jahr2 Then
MsgBox "Dreiecke von unterschiedlichen Jahren"
Exit Sub
ElseIf reporting_Jahr1 = reporting_Jahr2 Then
If Anfangsjahr1 < Anfangsjahr2 Then
'Sheets(Blatt2).Rows(3:3+Anfangsjahr2-Anfangsjahr1).EntireRow.Insert
**Worksheets(Blatt2).Rows(3: 3 + Anfangsjahr2 - Anfangsjahr1).Insert Shift:=xlDown, CopyOrigin:=xlFormatFromLeftOrAbove**
ElseIf Anfangsjahr1 > Anfangsjahr2 Then
Worksheets(Blatt1).Rows(3:3+Anfangsjahr1-Anfangsjahr2).Insert Shift:=xlDown
ElseIf Anfangsjahr1 = Anfangsjahr2 Then GoTo X
End If
End If
X: Next ws
End Sub

Answer 1

I don't follow exactly what you are trying to get to here but there are some syntax issues.
Not sure if this is what you want, but it fixes the syntax. Do you rally want
Worksheets(Blatt2).Rows("3:" & 3 + Anfangsjahr2 - Anfangsjahr1).Insert Shift:=xlDown, CopyOrigin:=xlFormatFromLeftOrAbove
EDIT to expand on OP's question in the comments below
The double quotes are used to enclose a string. So normally when you are referencing rows you can say .Rows("3:9").Insert This is providing the rows you want to work with as a string.
In your case you wanted to dynamically provide last row so we have
our string "3:"
transition from string to variable &
and our variables and math 3 + Anfangsjahr2 - Anfangsjahr1
To make up .Rows("3:" & 3 + Anfangsjahr2 - Anfangsjahr1).Insert

Answer 2

You need to place the row number in double quotation marks and then concatenate the variables to the string using an ampersand:
Worksheets(Blatt2).Rows("3:" & 3 + Anfangsjahr2 - Anfangsjahr1).Insert Shift:=xlDown, CopyOrigin:=xlFormatFromLeftOrAbove