You might've always wanted to learn language, or you may have just clicked on this website for the fun of it. Either way, you'll learn how to learn a language!
I am an A level student making this website for my project, and I know 2 languages (English and Polish) and I am currently learning Japanese.
I found that most language learning resources don't give great resons to learn a language, or don't even teach you as well as they could. Sure, learning a language for travel is nice, but all you're really going to learn is how to say "hello", "please", "thank you", and menu items. If you're fine with this, that's fine! Not everyone wants to spend their time (or even have enough) to learn a language. But if you're still interested, carry on reading.
If you have a specific language you want to learn, I would highly suggest looking up forums about the language or finding a webstie dedicated to linking resources. Online forums often can answer a lot of your questions and guide you better than this website. Each language has specific qualities which make it different from others, meaning a general approach wouldn't work.
The best way to learn a language is to immerse yourself in it. What that means is, try to watch movies in that language, listen to podcasts in that language, watch youtube in that language, so on and so on. The most important part of this so that it can work is that you cannot interact with a language you know while doing this. No foreign lagnuage to native language dictionaries, no native subtitles, nothing like that. It sounds counter-intuitive, as you may think "How do I learn a language without knowing what the words mean?". However, how did you learn your native language? Did you use a dictionary to translate into a language you know? of course not, so why do that now? Your brain is a lot smarter and weirder than you give it credit for.
While immersion is very important, you can't do it all the time, and with the amount of common words, you can't remember everything. The solution is flashcards. Specifically, the Spaced Repetition System. What that means is that for each time you correctly rember a flashcard, it waits longer before showing it to you again. It is supposed to mimic how memory actually works. For an in-depth explanation, you should click the "further reading page".