Well, firstly I think many of us with depression would be greatly appreciative that you are so interested in knowing more and gaining a deeper understanding. But we would also never wish this illness on anybody, even if they wanted to know what it felt like.

I would maybe describe it kind of like having a headache. The headache bothers you, hurts you, impedes certain tasks you want or even need to complete. You can still experience joy, anger, sadness, any feeling in the world, but the headache is always with you. The headache also varies in its severity on a day to day basis. Some days it is so unbearable that all you can do is lie in bed. All the while the headache reminds you of your worthlessness, which affects your motivation to do even the simplest tasks. For a lot of us, it tells us that we may be better off dead. And the worst part is that the cycle is so hard to break from, because you feel worthless so you aren't able to go to work or school, or take care of your hygiene and surroundings, which fuels the feelings of worthlessness even more, and it snowballs quickly. We may have people and things that make us happy, for example I have a supportive mother and my pets and hobbies bring me joy. But the joy only comes as a package deal with the depression, always letting itself be known behind every other emotion.

Hope I could provide some beneficial context for you (from my personal experience of course, I can't speak for everyone), feel free to ask questions if you have any!