So to start I did a coat of Essie Blanc. It's my favorite white I have because after two coats there are almost no streaks.
Then I picked a few of my cheaper colors since you do waste more because you have to pour out some of the paint to make it work.
I poured one color at a time onto a paper plate and then dipped the end of the straw into the paint. Hold your nails over the plate and give a quick puff of air into the straw while it's pointed at your nails. It took some practice for me and I learned to check that the bottom of the straw had a paint bubble across it before I'd even blow.
You will get messy and if you aren't willing to go back through with a q-tip dipped in nail polish remover I recommend you either tape your fingers or coat them in vaseline for quicker cleanup.
Super easy, somewhat time consuming, & very cute!