To get a reading, make sure you are....
1. pushing the test strip fully into the meter (the screen should change - mine shows a drop of blood when it's ready to go, but I have a different type of meter -- but somehow the screen should indicate it's ready to read)
2. poke the ear
3. "milk" the ear to get a little bead of blood
4. touch the opening of the test strip to the drop of blood and let it suck in the blood
5. wait for the reading to appear
From the time you push the strip all the way in, until the time you suck in the blood, you'll have a set amount of time. Depending on your meter it might be 60, 90, or 120 seconds. After that it will time out. If you end up needing more time (for example your cat decides to wander off and chase his brother), you can pull the strip back out, and re-insert it to reset the clock.
And yes, those clicky devices are useless. Most of us just use the lancet (the sharp part) and free-hand poke.
As for the interpretation of the reading - in a regulated cat (and it can take months to get to regulated), the curve should look like a smile. The pre-shot numbers will be higher, the nadir will be lower. So you inject, in about two-three hours the insulin starts to kick in, then the BG will start to go down, down, down, until somewhere around +4 to +7 (varies by cat, and sometimes by day), then the BG will start to rise again until it's time for the next shot.
As a cat gets well regulated, they will often drop on the earlier side of that range (+3 to +4), and then flatten out in the middle of the cycle (we call that surfing), and then rise again towards the end of the cycle. So still a smile, but a little flatter in the middle.
Looking at your numbers, it looks like you had an 800 for PS and a 49 for +3. While that's not impossible, my hunch is that one of those numbers was a bad reading. If the little window in the test strip has too much or too little blood, you can get a bad reading. So when something seems particularly out of place or dramatic (like dropping over 700 points in three hours), we usually suggest testing again to see which reading was wrong.
Anytime you get a lime green number, it's time to take action. Hypoglycemia can be dangerous. At 49, he wasn't hypo yet, but if he kept dropping for three more hours, he could be in danger, so it's important if you get a lime green number to follow the directions in the yellow sticky for hypos.