When you buy a foundation or tinted moisturizer, the important thing to know is that you need something for the foundation to stick to, especially if you have oily skin or live in that area that gets very warm. Even if it isn't warm in your area, a primer helps create a smooth surface for your foundation. It's very helpful for those of us that have a little texture to our skin.
I have two of my absolute favourite foundation primers: one from the drugstore and one that's higher end.
Hard Candy Smooth Envy Primer - Only $7-8 at Walmart, this is the best drugstore foundation primer I've used. You get a little more product than the average primer in the store. It goes on silky smooth, dries down nicely, and keeps my makeup looking nifty.
MAKE UP FOR EVER HD Microperfecting Primer - I think this one is actually my favourite primer of all time, but at $34, this is definitely not cheap, especially since this is a product that you would be using a lot. It smells divine, feels like silk on the finger tips and face, and goes on like a dream. It makes my face look smooth before I put on my foundation, or even just my concealer. This comes in many shades, but I always prefer the clear one. 0 is the "natural" shade and is supposed to add natural luminosity to the skin, which is something my dry skin absolutely needs!
If you have normal to dry skin like me, you may not need the help of a foundation primer to keep your foundation on, but like I said, it's really nice to help create a smooth canvas before putting anything else on your face. If you have combination/oily skin (especially oily skin), I highly recommend using a primer for both reasons.
Makeup 101 is going to be a series of blog posts telling you what sort of products I would recommend for certain things in a makeup routine. Later on, I'll probably end up writing some tips and tricks. Feel free to leave requests in the comments section!