How can I make my depressed friend better?
The simple answer is: You can't. If there were an easy way to fix depression, no-one would need to go through it. Your friend has probably been trying their heart out to fix him or herself, and getting nowhere. Healing for depression is not an instant process, there is no magic switch to flick and make everything sunny again.
There is some information on this page about how to help in depression, but basically, you need to support and pray for your friend. If they have not seen a doctor, you should encourage them to do so.
Do not expect your friend to get better overnight, be patient with them, show your love and care for them. Spend time with non-depressed people to recharge your batteries.