I have two magento2 application running which are M2(a) and M2(b), I want all product on M2(a) to be displaying on M2(b) automatically, I have created an Integration on M2(a) by going to admin->systems->Integration. and now i don't know how to call the key generated on M2(a) and integrate it on M2(b). Any assistance will be highly appreciated
I think there are many individual ways how to achieve this. This can be done either trough API communication where one store consumes the Stock and Product Set of the other, or by sharing a common Database, or having access to the "others" database and use the additional connection to read. However, all of this requires a lot of development and is - as far as I know - not possible out of the box.
The easiest way is probably to create two Websites inside one Magento Application, so that Store A and Store B share the same core of Magento2. The two individual Websites inside Magento2 must be configured accordingly and eventually share a Database connection, and Products can be made available to both Stores. This is a core function of Magento2 and requires - for basic functions - no extra development.