RIP I've suffered from severe depression and it's not joke. I've reached a point where I understood why someone could take their own life. Luckily I had already been diagnosed and educated, so I understood that things would eventually get better.
When I try and describe severe depression to someone, I usually say something like; imagine waking up every morning and feeling like everyone in your life was dead, only they weren't. Then wanting to do everything you love to do, but being completely unable to. It's a deep feeling of emptiness and discontent with everything and everyone around you, to the point that is unexplainable unless you've experienced it.
I think the most important part of dealing with depression is recognition and education. The problem is that people experiencing depression are ashamed of their feelings, and tend to both physically and emotionally isolate themselves from friends and family. I was able to defeat my depression without the use of any medication (plenty was offered), but it took about a year of my life.