connecting a motion sensor and an air pump to an Arduino

For a university project, a couple of students and I are attempting to create a jacket that inflates when people come close to you (whilst wearing it).

We're planning on using some kind of motion sensor (we're not sure which one yet) and an arduino uno to alter how much power a 12v electric pump puts out (gradual not binary) depending on how close it is to something/someone. Unfortunately none of us have any knowledge of circuits or programming.

How might we go about connecting all of these components??

Thank you for any help you can give.