Bigger feet means taller sims, smaller means shorter sims. To use the mod in the game, all you need to do is drag the feet of your sims. Both version will let you change the height of teens and adults. Teens at the end of the name means teens are generally shorter than adults. If you dont know which one to choose than I recommend heightslider1(teens) as the others can be a bit massive and their portaits will look strange. If there are only one number that means both are the same scale. The 1525 means the heights are 1.5 times shorter than usual and 2.5 times taller. They are all named heightslider then a number than with or without teens. The are several different versions of the mod. (I can not do anything about the kissing looking weird for sims with different heights etc, as this requires to change the animations a LOT, and if it were easy i would think the sims team would have already implemented it) Only thing new is that the animation is no longer as funny looking. This is a height slider based on simmythesim first height slider. Remove the old one and place this in your mods folder unzipped I added the fix to one of my downloads (heightslidertoddlerfix), and will hopefully add it them all once I have more time.
A toddlerfix is made by vectorplexus for the old sliders by simmythesim.