My question involves collection proceedings in the State of: California

Hello, I own a $20,000 student loans. I don't have any job, therefore I have no income to pay them back.
I also don't have house, no car. I feel that soon they will send a debt collector after me. What will happened then? I heard many horror stories like debt collector fake pose as police come to people house. And so many harrass stories, it kind of scary.
So let say if the Department of Education where I get my loans send a debt collector after me, would they tell me and let me know first?
How long can a debt collector bother me? Is there any websites that I can read more about this?
Thank you