Replace the smaller top pin into the frame (obviously, 9mm's skip this step)
Place the lower, large pin about half-way into the frame as shown on the photo to the right

With the lower pin only half inserted, replace the slide release back into the pistol. It's proper position is in between the frame and the trigger, as indicated by the red arrow in the photo on the right. The little wire spring of the slide release sits underneath the first pin, which is why it is replaced first.
Once the slide release is in position, press the larger pin into place. It should not stick out of one side more than the other.

Photo of assembled frame.

ASSEMBLE THE SLIDE
Start out by putting the firing pin back together. Place the firing pin in it's plastic sleeve as shown in the photo on the right.

Place the spring over the firing pin as shown in the photo on the right.

Depress the spring (you can also cheat on this step by using cleaning cloths or whatever) and replace the two parts of the collar. The spring should slide over the collar and hold it in its proper position.
Photo of firing pin assembly.

Replace the extractor plunger and spring. Press down on the plunger and replace the extractor. Release the plunger. It it was inserted correctly, the extractor should stay in position when the plunger is released

Place the firing pin assembly and extractor spring assembly back into the slide as shown on the right.

Press down on the firing pin assembly and begin to slide the backing plate back on. Use a small punch to push down the extractor spring assembly and fully replace the backing plate. Ensure the plate is fully seated.

The slide is now assembled!
Test the slide for function before replacing.
Press down on the extractor plunger and ensure the firing pin can move freely back and forth. Release the plunger and ensure the firing pin cannot be pushed forward far enough to be exposed. If everything works out--you've done everything correctly!
You may now assemble the pistol in a normal manner.