SPI is not that difficult. in fact,it is the simplest protocol ever. there is no error checking, no parity, no acknowledgement, nothing. so easy to understand. You just need to learn its modes and always remember, SPI is a data exchange protocol. So if you want to receive something, you have to send something.
for better understanding, you can make circuit of MCP3204 and PIC16f. You can easily get their interfacing diagram on internet.
Once you write the code, u will come to know that it is much simpler than I2C.
All the best