how to use the poll feature inside the post reply or create a poll post ? 

Polls are added to the topic itself and will appear above first post. 

The forum and the user group must have permission to use polls.

If it is an existing topic, user mist edit first post and then add the poll.

I open the poll permission to admin and others user group still cannot use polls. I cannot see any poll function can click 

12 hours ago, Adriano Faria said:

Polls are added to the topic itself and will appear above first post. 

The forum and the user group must have permission to use polls.

If it is an existing topic, user mist edit first post and then add the poll.

even I add the poll permission to admin also cannot see the poll option

You would click on "Start new topic". The poll is inside there