How do you get rid of pimples on the nipples?

They are most likely Montgomery's Tubercles. These are sebaceous cysts that produce sebum-oil that lubricates skin. They are common and normal appearance on areola. They protect the skin by lubricating it and also have antibacterial function.

They become more evident when hormonal changes occur during puberty and pregnancy.

They are normal and most people have them and could squeeze white stuff out of them if they tried. It's normal! Don't be embarrassed! But, best not squeeze them too much or they could get infected.