How do I start (learning) programming with an actual project in mind?

Maybe here is somebody who can help me. I would like to start programming on a project I thought about since a year or so.

The project is going to be a web app which is also going to be used via iOS and Android Apps.

The software is going to be recommend different training-modules and show your progress thourghout training.

So what is the best way to start? Where can I find ressources on planning a software, a datamodel, the workflow and user experience…

And the most important question is:
How do I start in front of a blank sheet of paper – err monitor?

Thanks and greetings from Germany,
Alex