I did my nails like this the other night after seeing something similar on Pinterest. I didn't find any directions to follow, but it's really pretty simple to do so I thought I'd share what I did! I tried taking step by step photos but it's super hard to take photos of your nails as you're painting them :)
TIPS BEFORE YOU START:
You want to use two nail polishes that have similar brush sizes and shapes. A lot of my newer polishes have a square brush that doesn't really work with this look. It's also best if you can use polishes that only need one coat.
1. Wipe off most of the polish from your brush on the bottle. You don't want a lot of polish to drip down as you paint. Dip your brush back in until just the tip has a little glob of polish. You need it to be a round-ish droplet in order to get the scalloped look.
2. Paint your scallops on your nail! I like to do them staggered because it's easier to define the shapes than if they were all in a line. Just use that little droplet to make a circle on your nail and then pull the paint towards the tip.
3. Let your first coat dry completely. Paint your second color the same way, leaving a little space for your first color to show through. If your second color scallops don't connect to each other, just fill in the space once you've done the rounded part. Let it dry and seal with a top coat.
Like I said, pretty simple :) Let me know if you give it a shot!