I want to use Mikrotik Radios to link all our branches together, to transmit these financial data 1) how do I make it secure and 2) is it possible. I only know about using Mikrotik to share Internet connections.
Yes this is not a problem. You can do MPPE128 bit, 3DES, even AES 256 if you wish. And you can share the connections. I would recommend to contact a MT Consultant though as some of these setups can get to be quite a bit to explain in a forum.