1.        How to calculate users number in Office 365 admin https://portal.office.com/admin/default.aspx#ActiveUsersPage ?
2.        How to export users from Office 365 admin?
3.        How to add selected users in Office365 admin to group?

Hi,

In this forum, we mainly discuss questions and feedbacks about Office client. As the questions are about Office 365 Admin, I'm not the best resource to answer the questions.

Anyway, I hope the information below will be helpful to you:

Getting all Licensed Office 365 users with PowerShell

Create and use distribution groups

To get the best support about Office 365 Admin, I suggest you post the questions in Office 365 Community forum:

http://community.office365.com/en-us/f/default.aspx

The reason why we recommend posting appropriately is you will get the most qualified pool of respondents, and other partners who read the forums regularly can either share their knowledge or learn from your interaction with us. Thank you for your understanding.

Regards,

Melon Chen
TechNet Community Su