adjust your meter. And now for a real answer to the OP.
To get smooth slow motion (without using twixtor), your camera has to shoot in a frame rate greater than 24fps. Typical framerates that most cameras shoot in (outside of stuff like the Phantom Flex, etc.) are 24, 30, or 60 frames per second. 30fps will give you subtle slow motion, while 60fps will be much slower. What you have to do is conform your 30 or 60fps footage to 24 fps using some kind of software (I use Cinema Tools), but there is probably something free that will do it, just use Google. Then you can import your footage into a 24fps timeline in your editing program, and it will play back in slow motion automatically. Just split the clip at where you want it to change speeds, and change the speed of the first part of your clip to play at normal speed (250% if you shot at 60fps).
As far as those fancy pictures with a bunch of people doing the same trick right behind each other, that is called a sequence. You will need a camera that has a relatively fast continuous shooting mode if you want to do a jump sequence. Probably at least 5fps. You will have to shoot in full manual mode, to avoid discrepancies in exposure between each shot. Then you can put each photo into a layer in a photo editing program like photoshop, and arrange them so that they line up.
Sorry if my answer isn't all that helpful. I'm a bit drunk. I'm going to sleep now.
