How could i create a function that would aways show me last
workday before today? so for example:

1.today is wednesday 15 jun. So the function would show:
tuesday 14 jun
2. today is monday 13 jun and the funtion would show:
friday 10 jun

Try this formula...

=WORKDAY(A1,-1)

If you are using XL2003 or earlier, then you need to have the Analysis
ToolPak add-in selected (Tools/Add-Ins on the menu bar).

Rick Rothstein (MVP - Excel)