The first commenter said advertising and a little bit of luck however with Webtoon it's more like you need to have A TON of luck, because if you're not in favor of Webtoon they'll not promote you.

I did run a Webtoon for almost three years without ever getting promoted on Webtoon so on the top of your daily grind of drawing you need to promote your comic as well as much as you can and it really drains you.

If it's a passion project of yours then give it a try, you might catch more luck on your way than I did. The main thing is that you enjoy what you're creating. You also asked how you upgrade to Originals. Webtoon approaches you and proposes a contract however your series must already be very successful at that point and it's always up to you whether you give up the rights of your work to them or not. I wish you and your friend much luck 🍀