VBA: Change content of each sheet in an workbook

[bongus]

Hello.

I am new to this forum and hope for a little help.

I have searched the forum have, to my surprise, not found anything quite similar to my request. Perhaps it is too obvious?

For every sheet in a workbook, I would like to replace cell contents. It is always the same for each sheet and the structure of each sheets is the same.


I tried some permutations of the following syntax but to no avail.

Sub test()

For Each ..... In .....
       cells(1,1)="New message"
       cells(1,2)=<formula>
Next
End Sub

Now there are two questions:
1. What should I use to replace the ..... ?
2. How do I specify a formula (where formula I want in C5 could be "=if($C$1="OK"; A5+B5; 0)" ?
Edit: Figured the second one out.

Extra bonus: How to do this for all workbooks in a directory or in the current directory.

Optionally: If it is simpler, it is OK to copy a range from a template and paste into all sheets.

Best regards