Withdraw from my 401k?

Okay so I am in desperate need to taking money out of my 401k plan that i had with my previous company that i no longer work for. I still have a job, but I have bills on top of bills i never thought i would be in this position. I getting bills from the emergency room, doctor, my school that i really want to go back to, but becuase I owe them i still cant attend. Everyweek when I get paid literally its gone within less than 48 hours and im left with like 50 or less for the whole week. I have a medical bill that now $2,205 well it was $6,000 but got it down to that amount. Im only 26 and i cant believe this is happening to me, im so overwhelmed and on top of that i have rent to pay! my 401k at my previous job only has $1,518 in it. I hearing all these things about 10 percent penalty is it worth it. How does it work? Do i pay the 10 percent when i withdraw from the account, do i pay for it when i do my taxes. And if i do withdraw how long does the process take? are their any forms to fill out?