21 days' clear notice for AGM

As Per my understanding Clear Days meaning All the days in a schedule or in timeline, except the day of commencement and day of completion.

According to clear days meaning the day of sending of notice  and day of meeting is excluded i.e. 2 days 

according to act proxy form will be deliver to company before 48 hour from the meeting so 2 days for proxy form.

Now the total time period is  25 days

21days :- for notice

1 day :- sending for notice

1 day :- meeting

2 days :- for proxy form

Can someone explain to me a little about AGM and the importance of an AGM?