Can Any one Please Advise me on this Topics:-
1) How to learn PWA in magento 2 ?
2) How to integerate PWA With Magento Custom Theme ?
3) How PWA Works in magento 2 ?
Please refer PWA devedoc Documentation. I am sure you will get enough knowledge about the integration and PWA-studio and Custom Theme. Here is the link :
Or you can join Magento official Slack channel for PWA in which you can do Q and A.
Use Hashtag #pwa.