Ok.
First, there should be 3 of them. I only see 2 in the pic. Find the other one. there should also be 2 C-clips as well. Very thin, metal wire loops with a little straight piece on the end. What you have to do is assembly the outer gear with the inner gear, the slide the 3 keys in with the dent facing the inside. Slide the synchro in with the tapered end in. Then place one of the straight segments of one of the clips in a tiny hole near one of the keys.rotate it around until you find that tiny hole. Then you bend the clip in to the I'd of the gear. The clip wants to act like a clock spring and holds the keys in place. But watch, the clip needs to contact all 3 keys, if it only contacts 2 of the, you gotta flip it around. Once you get the first one in, flip the gear over and do the second one clip on the other side. You should see that the clips capture the keys by not letting them slide past the shoulder of the key.
If you need more clarification , let me know.