If you search the
net for documentation about SPI interfaces will you properly
find some good descriptions of aspects, concerning the interface
and connections between SPI - Master and Slave devices.
However must you
realize that this merely "the tip of the iceberg" - in order to
be useful must both Master and Slave(s) have built in logic,
in order to interface with the respective systems.
versions above and realize the problems you must solve in
order to create good SPI interfaces.