I can't understand the part of returning value for function while not in stored procedures?

Hi Islam!
Thanks for reaching out.

The idea is that with stored procedures, you need to think of where to store that value (e.g. - the 'output parameter' shall act as a placeholder for such a value). Also, this value can be of many types - sometimes a single numeric value, other times - an entire table.

With functions, you can only return a single value.

Hope this helps.
Best,
Tsvetelin