I think I know someone suffering from depression.
I had it one time, Depression is a state of low mood and aversion to activity that can affect a person's thoughts
Is there a way to get help for depression?
i would go to the doc, A depressed mood is a normal temporary reaction to life 
What else should I know about depression?
i have heard  It is also a symptom of some physical diseases and a side effec
Oh wow. I did not know that. 
yeah you can tell beacause People with a depressed mood may be notably sad, anxious, or empty