Starter wire: black/white
Ignition wire: black/yellow
Both wires are found at the ignition harness coming off the steering column.
You clip the starter wire (black/white). Your then left with 2 ends (starter and ignition switch). Wire the end that goes to the ignition switch to 87 on the relay (diagram says key side of starter). The other end goes to 30 on the relay (diagram says motor side of starter).
You need 2 spdt (single pole double throw) automotive relays, momentary contact switch (make sure its momentary, you don't want a on-off switch), wire, crimps (female spade / disconnects, solder, etc...
Make sure you understand the diagram. If you wire it up wrong, the car won't start and/or you'll end up shorting something out.