Create Instant messaging app like whatsapp or youtube?

I love chatting and sharing photos and videos with my friends on social media, but lately I'm thinking a lot about creating my very own Instant messaging app. So, how does one go about doing it?

>>3
You're missing a lot of factors here. How will you handle cases where the string is misogynistic, racist, homophobic or bigoted? What if it's offensive, harassing, or inciting violence against the string's recipient? What mechanisms will be in place to prevent disclosures of intellectual property?

And this is just scratching the surface. I doubt you've seriously considered the problem specifications here.