Super simple and annoying issue: have a written programme in VBA, how to activate

Guys,

I'm asking for your kind advice on this extremely annoying problem. Never really liked and learned VBA, have to use it for a small task. I am using a readily-available code from the Web that defines a programme. I copy the code from the Web, paste it into VBA, go to Sheet1 of the Excel document where I have some data, try to type the name of the formula so that I can use it and it does not work. The name of the formula does not appear on the suggestions, obviously Excel does not recognise it.

I used that same piece of code before (it worked OK) but really forgot how I made it work. Any help is appreciated.

Thanks in advance!

May God bless you, good man!