input_event structure description (from linux/input.h)

The struct input_event is, among others, defined in include/linux/input.h.

From 5. Event interface in Linux kernel Documentation/input/input.txt (and modified to provide the correct header file names):

• time is the timestamp, it returns the time at which the event happened.

• type is for example EV_REL for relative moment, EV_KEY for a keypress or
  release. More types are defined in include/linux/input-event-codes.h.

• code is event code, for example REL_X or KEY_BACKSPACE, again a complete
  list is in include/linux/input-event-codes.h.

• value is the value the event carries. Either a relative change for
  EV_REL, absolute new value for EV_ABS (joysticks …), or 0 for EV_KEY for
  release, 1 for keypress and 2 for autorepeat.

For guides and example code, do a web search for "linux kernel" "input subsystem".