The answer is actually more basic than most people expect: immersion. Language isn't acquired in a classroom, or through apps or textbooks – it's acquired in the real world through interacting with real people. This is while children often learn their mother tongue before they begin formal schooling, by virtue of the fact that it's being spoken around them. Their subconscious is absorbing everything they hear, and this will slowly develop into an active command of the language.
- Watch movies. Have English subtitles as well. This is often a good starting point as you can benefit from the experience even with no prior background in the language. Slowly, you vocabulary and understanding will build.
- Listen to music. This is helpful because songs get stuck in your head, which means you'll keep singing it over and over, and the structures/words used in the song will become ingrained in your memory. Of course, find a translation of the lyrics as well.
- Listen to the radio. Once your confidence and ability increases, start listening to longer readings of texts. I suggest this first since some people might not yet be comfortable interacting with other people, and this serves as a safer space to improve.
- TALK TO PEOPLE. This could actually be the first step if you're brave enough. Interacting with people face to face will let you experience the language in different environments and situations, adding to both your vocabulary and complexity of sentence structure. You will also learn how to better understand when someone else speaks the language (colloquialisms, speed, etc.). Usually, native speakers of a language are more than happy to teach, correct or advise you on the spot, so in some ways, it's a free lesson!
Personally, I prefer going for classes, at the very least on top of all the above. This is because I tend to be a perfectionist, and so I like for my command of the language to be of a certain standard before I use it in public. Even in such a case, though, I recommend you try finding group classes, since it gives you a chance to interact with more people, rather than just one teacher.
My emphasis on immersion is why I usually discourage the use of apps to study a language. While it provides you with a resource you can refer back to, it doesn't give you a chance to actually use the language in any useful way. By all means, download whichever apps you feel necessary. But make sure you complement them with the above methods.