Contacts and tasks missing from Gmail app

I am somewhat new to Android. I would like to know why the Contacts and Tasks functionality which is found in the web version of Gmail is missing from the Android Gmail app. Where can I find these? - I could look for my Gmail contacts in the Contacts stock app, but it shows all contacts, not only Gmail contacts, and I can't filter these so as to show only the Gmail contacts. - Also, there is no Google Tasks app on Google Play. What's the best way to view such tasks?