Ok now, this is seriously my favorite part of skin care.
Your skin type, degree of dryness, oiliness, enviroment, lifestyle etc... will have a lot to do with what you need out of a moisturizer!
I will try to keep this as simple as possible by explaining the most common "types" of moisturizers so you can choose the best one for you at a certain time, you will not need the same moisturizer trough out your life, but rather you will need to meet your skin needs depending on what your skin is asking.
Hydrators: These will offer water content to your skin. More likely you will notice fine lines, dullness, and sallowness if your skin is dehydrated.
A hydrator will have ingredients like glycerine or hyaluronic acid, the texture tends to be light and "watery" or have a gel like consistency. Oily, dry, and combination skin types will benefit from hydration!
Moisturizers: These will add oil to the surface of your skin providing comfort to dry skin types. If you need a moisturizer you will more likely feel like your skin lacks a glow, tightness and discomfort mostly after cleansing your face. Look for ingredients like almond, olive, argan oil and thick textures. Oil rich moisturizers are a must for winter time if you have dry skin.