How to join different subnet ?
a: 192.168.2.1/24
b. 10.7.7.7/24
I wanna between A and B can be share(print and file sharing) 
, iam very new bie
That has nothing to do with subnetting. Subnetting is when you change the netmask of a network to make the network smaller or bigger. That is - for practical purposes - impossible between the networks you have.
If you’re talking about Windows filesharing and printing you can do so directly by IP address if both of those networks are on the same router. If you need to be able to do so by name you either need an active directory domain controllers, or a WINS server.
so, what must i do
futher line A and B , can be PING
Configure two router interfaces for IP addresses in those networks (the IP addresses that clients use as their default gateway), plug the networks into the appropriate interfaces - that’s it. The router will then route between those networks.
You may want to read up on TCP/IP fundamentals beforehand.