You can use this in many ways, and colour ways. I like to use actual sellotape / scotch tape rather than cheap tape because its a little thicker and you can see through it and therefore can see if it is stuck on properly so the polish doesn't bleed underneath the tape.
Before you start if probably a good idea to precut enough tape, so you don't end up smudging the polish
Start with your nails painted, I've used ELF - Mint Cream. Wait for this to fully dry before moving on to the next step. If you are impatient a fast dry top coat will help.
Stick the tape on to your nail in whichever patter you choose, make sure there is no bubbles
[and yes I edited the contrast so you can see the tape]
Paint a thick coat of a contrasting polish, I used Barry M - Racing Green. Do one nail at a time, and as soon as you have painted the alternative colour pull off the tape. Must be done while the polish is wet in order to get a crisp line.
Repeat on all the nails however you want. You can see I haven't done this perfectly but practice makes perfect!
Finish off with a topcoat to make everything shiny and less bumpy.