me and group of colleges are working on app that connects to OBD device and displays that data after working on it, but we are facing a problem on understanding what is the data received by the phone if it connects with the device via Bluetooth and its form.
after some research all we could find was that data can be of hexa form but that did not help us to fully understand the process. if someone can kindly help us with some resources or description that would be appreciated.
OBD2 itself is documented in various ISO standards, which you probably want to obtain and read. The guts of it is a protocol where you send a PID to an ECU and receive the result. Different PIDs have different meanings and are encoded in a certain fashion, which you can learn from the ISO standard (or Wikipedia, which contains an excerpt).
Since you have mentioned Bluetooth, you probably have a generic serial adapter based on an ELM327. In that case you need to learn about the ELM327-compatible AT commands which are necessary to setup the communication and adjust the addressing.