Creating a GPS Tracking App from Scratch. What Should Come First?

Hey everyone, My name is Nick,I’m a high school student working on a personal project. I want to build a GPS tracking app, something similar to Strava. To be honest, I’m a little overwhelmed about where to start and what order I should tackle things in.

Since this is a solo project, I’m pretty sure I’ll be handling almost everything myself, from planning and UI design to development, server setup, and testing.

For those who have experience building apps, especially mapping, fitness, or GPS-related apps, could you share what you think the development roadmap should look like?

One feature I definitely want is real-time team tracking, so users can see their teammates’ locations during activities. I’d also like the app to send notifications if someone has an accident, such as a fall while cycling, or if a teammate gets too far away from the group or the planned route.

Thanks <3 ( btw sorry for my grammar ,it’s terrible )