This is a subject that can cause many cat owners to be very concerned. While constipation can cause troubles in some cats, you should never attempt to relieve this without professional guidance.
Giving your cat mineral oil or other home and over the counter remedies without specific medical guidance is ill advised.
Cats can get much more sick from inappropriate attempts to relieve constipation. If you are concerned that your pet has not defecated in several days, then you should go see your vet.
This is especially true if your cat is not eating, vomiting or seems lethargic and not themselves. If they are acting totally normal then you should look and see if they have pooped somewhere other than the litterbox.
If you are not sure, then a call to your vet may be a better option if they are acting otherwise fine. They may advise some simple tricks to get things moving.