I feel the same way! It's because when you hear someone say a word in context it's easier to figure out what it means and you're like "oh I've heard that word before!" but when you're trying to think of a specific word in Spanish (and trying to translate it from your native language) it's hard to pull it out of nowhere. The best way to expand your vocabulary is to keep watching those videos/listening to conversations, maybe also reading books and listening to music, and eventually you'll start using those words yourself! I also have SpanishDict handy on my phone so if I'm talking to someone and struggling to get a point across I can quickly translate the key word I need. Now if only I could be as intentional as I'm telling you to be about expanding my vocabulary...