RFM69 Transmit and Receive
Here is the manufacturer's page for the RFM69.
It should tell you most of what there is to know about it.
(I see that that site is where you got the RFM69 data sheet  from). 

From the datasheet, the following diagram on page 76 sows the general method ofs use.
You will usually need two of these.
Translating that into an 8051 based version should be easy enough as far as hardware goes.



Page 76, Fig 41



This block diagram from page 8 shows what happens inside the IC.