Okay there are a few things you can go to prevent your paper from wrinkling.
1. Stretch your paper- what I use is Masonite board (you can get either at a hardware or art store, they have different sizes depending on how big or small you want to work) paper tape (which sticks when you wet it, like an envelope seal. What you need to do is place the watercolor paper on the board, and use a spray bottle filled with water to dampen the paper. This prevents it from wrinkling when working and allows it to dry flat after you have stretched it. Get a sponge and a cup of water so you can rip off strips of paper tape, wet them, and place them down on the edges of your paper. Make sure your pulling the corners of the paper while you're doing this (hence the stretching) so it's as flat as you can get it. If it's not flat after you stretch it don't worry, it will flatten when it dries. If it's not flat when it dries you may have done something wrong. Try to watch a youtube tutorial on it or something. Once you are done creating your piece you can cut it out with an exacto knife and it will be nice and flat :)
2. There are these things called watercolor blocks. The brand Arches makes them They are 10-20 sheets to a block. You can work on those and once you are finished you cut it out with a palette knife and it should stay flat the whole time you're working. A couple issues with the block is A. They are really expensive (I've seen them between $35-$45) B. they don't always stick to the block, the water you work with can seep through and cause it to come undone on it's own.
3. Try to find a thick board like a 400-500 lb watercolor board. Or sometimes you can also find pre stretched watercolor paper.
Stretching your paper is probably the cheapest route to go, I wouldn't recommend getting a block or a fancy board unless you're doing a really important project.