For me, a makeup primer is an essential in my makeup routine. A primer preps the skin before any makeup application.
Primer will help your makeup last for hours without seperating. All you need is a tiny amount (think pea size) & I apply it on my forehead, nose, cheek area (avoid under eye) & chin, basically anywhere you normally see your foundation start to separate.
Primers also help absorb any oil on your skin, which is ideal if your skin is oily. This will help reduce any shine. You can also get an oil primer if you have dry skin to hydrate.
It reduces the look of your pores, especially if you have large one, helping to close them & also smoothes your skin.
They fill on lines & wrinkles on your skin. It really makes your skin feel velvety smooth to touch. I always leave my primer to set for about 5 minutes before applying any foundation or makeup.
Some primers are available in colours to counteract any imperfections on your skin, e.g. buy green primer to hide redness on face, lavender primer to hide yellowness etc
There are a lot of brands who have primers but my favourite two are L’Oreal infallible primer for those on a budget & Smashbox finish primer for those who want to splurge.