Microphones don't just pick up the sound floating through the air, anything that they physically touch also transfers sounds. This means switch clicks, noises when you bump things, motor noises, traffic rumbles through the ground, etc.
You've got two ways to minimise this: Put the microphone on something very heavy, solid, immobile, and leave it alone. Or mount it in a way that isolates it from other movement. The latter is what a shockmount attempts to do, because the former is almost impossible to manage (even if you don't need to touch a microphone, noises can still be transmitted to it through the floor).
Don't forget to have a loose loop of cable between the microphone and the stand, with the cable anchored to the stand (as in the picture). Else, the cable will act as a mechanical transmission point of noises. I've seen people completely invalidate the purpose of using a shockmount by stretching the cable tightly between the leg of a floor stand and the microphone. You can improve the isolation, even more, by using a very light-weight cable for the loop between the mike and the stand.
Some microphones have an internal shockmount. The actual microphone element isn't rigidly attached to the body, it's suspended or mounted in something soft. This allows you to hand-hold the microphone, and not generate loud noises by doing so (rattles, squeaks, or even picking up your pulse). But most microphones are susceptible to mechanically transmitted noise, to some degree, so using an external shockmount is advisable. Especially when mounting a mike on a boom or stand, as that mount may make noises itself.
Expensive microphones often have their own shockmounts, specially designed just to suit them. But if it doesn't have one, you can make your own shockmount, or buy generic shockmounts that will fit a variety of different microphones (there's an illustrated review of a RØDE SM5 generic microphone shockmount in my website's reviews section).