As someone who has had depression since childhood, hopefully I can shed some light. I've been in therapy and medicated for years, and am in a safe and loving situation now, but symptoms are about the same for me. Everyone experiences things differently, but I believe these are pretty common.
Extreme loss of motivation and energy, even hobbies that were enjoyed seem daunting and pointless "It wouldn't be good enough anyways, so why bother", "I'd spend hours and end up sore with only a mediocre result to show for it", etc. Self care, hygiene, and environment maintenance is difficult, something I have to force myself to do, and it's exhausting. I'm always more tired after a shower, brushing my teeth, washing laundry, etc.
Even when I'm watching something, playing music, playing a game, doing something positive to keep my focus, there is still the negative track of "you're not good enough", listing my flaws, reminders of embarrassing things and times I was at my lowest. If I'm doing alright, I can ignore it, but when I'm feeling bad I'll ruminate on all the negatives.
As for suicidal thoughts, it's the same. When I've messed up something, the first thought is "of course I'd fuck this up, just like everything else, why am I even here". There are times I'm genuinely having fun, enjoying myself and time with others, where I get hit with "I don't deserve this, I don't deserve to be happy, I shouldn't be here". It's hard to let myself be happy, there's a deep guilt for just being alive and taking up space.
Not everyone goes to therapy or starts medication, but it takes work to combat depression. The negative thoughts and feelings won't go away, they may remain automatic responses, and you have to push yourself to counter them