Expert advisor question

Hello;

I can’t figure out something about expert advisers. Specifically, my question has to do with the magic number. Lets say I have downloaded a simple moving average cross EA that opens and closes positions. The EA’s first input is it’s magic number.

When I load the EA, what happens next? Do I have to place the EA on every pair and every time frame with a different magic number for each pair and time frame?

Can an EA be saved as part of a template and applied to multiple charts with the same magic number?

The more I read about magic numbers the more confused I get. I’m hoping someone will make it all really simple for me.

I am demo trading only at present.

Any help would be appreciated.

Regards,
Ian