You start with an innovative idea but you can always just join the fish and make a site / app that is already out there and the revenue cake is big enough.
You will need a pc or a laptop to create your idea or the ground breaking app.
I'm sure you will want to upload your idea using a high speed internet connection.
No doubt you will need some kind of perfect hosting to upload your site files to.
if you have some webmastering skills you won't need much money to start, no need for smartphone at start.
The other thing you need and it is not in the list is a steady connection to wjunction.com to share your ideas and ask for help, some of the most talented people I know are part of the community here.