Well, the "web stack" is basically html, css, javascript, php and sql. You can use those to make websites, web apps and even mobile apps to some degree. Then it's good to learn things like wordpress and website administration too. It sounds like a lot but some of them are pretty easy and also it does provide some variety. It's not really particularly daunting once you just give it some time and learn from good sources.
Other popular languages are ones like Java, C#, Kotlin, C++, Swift, Python... and many others. But it really depends what you want to create and what kind of environment you want to work in. They're all used for different things and have somewhat varying levels of demand. Also some often require more formal qualifications (like Java and C#) and some often require maths (like C++ and Python).
Also (sorry to ramble on, lol) some are more difficult than others. Java and C++ are quite tricky, for example. But most of these languages are fairly similar overall.
