Step 1 - find a base color. Make sure it is light enough for a top color and black to go over.
Step 2 - this shows my colors and the teeny tiny brush I used to trace
Step 3 - if you have ever done a cloud mani this will be well understood. Start about half way up the nail, paint a line down
Step 4 - take the next line about half down from the first on step 3. It looks kinda of like a heart on its side
Step 5 - take your fine brush and trace the top of the heart