Hi, Javi!
The computers make it easy for us.
This phrase says that the computers lighten something (maybe life or work) for us. Without context, we don't know what this IT means.
He could make things very difficult for us.
This phrase says that he could complicate things for us.
Exercise can make a big difference to your state of health.
This phrase says that Exercise can affect a very different way to the state of health.
to make it (or something) easy = to lighten, to facilitate
to make it (or something) = to complicate
to make a difference = to differ, to lead to different results
Hope, it will help you.