This website also has a code editor to test references and see how they look to the user. After creating an account, the user can choose the programming language they want to learn at the desired level of difficulty, ranging from Very Easy to Expert. To help you remember what you have learned, you can take notes along the way that will be saved in your account. There are tons of free resources available, whether you want to master a new programming language or start a code-based project.
FreeCodeCamp is a US non-profit organisation dedicated to helping people learn to code for free. They offer certifications and customised learning paths based on the technology features you're interested in. If you're more into iPad and iPhone apps (or just want to learn about them), check out Apple's tutorials and documentation here. On this YouTube channel, you can find free content from the creator of Code With Mosh (where he also offers paid courses).