First though, there are two kinds (at least) of depression. One is the normal kind where you feel blue when things go wrong in life. This is normal and it should fade. There is another kind related to an incorrectly functioning brain. For this medication is needed to help correct that problem.
When a malfunctioning brain combines with things not going your way in life... you get a high probability of a downward spiral and suicide. It's a terrible self-feeding cycle.
Back to technology: Having a sense of meaning and purpose is quite possibly the most important component to a healthy human experience. When you are completely down in the dumps, just going down to a local soup kitchen and offering to volunteer for a day can recharge you and spark understanding of the human condition.
What you can do with technology is endless. For instance, I have never encountered an app or site where I enter a zip code and see everywhere I can go and help other people that day, right then and there. If such an app or site could list close by "AA" style depression sufferers meetings I could drop into anonymously on my way to they metaphorical "soup kitchen"; that would be even better.
You won't ever understand depression through tech, but understanding it through the human side will allow to you to envision how to use your tech skills to help.