Even the biggest program starts with an idea and is written one line at a time.

The best (perhaps the only) way to learn how to write real-world programs is to start doing it. When you run into problems, you search the web or ask here for solutions to those problems. Eventually, you'll gain experience and have to ask less often.

However, there are some things that you should be aware of right from the start:

• Hardly any big application is written completely from scratch these days. You can get much more done in a much shorter time if you use existing high-quality libraries and frameworks. Getting started with these often feels quite frustrating and more work than doing it yourself, but that's almost never really true.
• Thinking carefully about how you structure your program (how to design it) is very important once your programs get bigger. Spend some time on that, and read some books about design (I'd especially recommend "Clean Code") and software engineering as well as about technical basics.