Do i need pro version to see and use calendar

No.  The only difference between the pro and free versions is the number of email accounts you can load, which is 2 with the free version.

No. You can integrate Google calendar with version of EM Client.

Yes, Warren is correct. Depending on what your email provider offers, you can either have your email/calendar/contacts all set up as a single account as with Google or etc., or you can add the different protocols separately…

If you need more help, let us know who your email provider is, and someone will be able to give you more info on how to set that up.