$400 a week is about $20K a year. That is very low income. Most professional jobs start out around $30K to $35K. I'm guessing you do not have a college degree?
You CAN live on $20K, but you would need to live very frugally. You should save up some money for deposits and furniture. IN ADDITION you need to save up a cash emergency fund of 3 to 6 month's expenses. Since you take home about $1,200 a month, you would want between $4,000 and $7,000 in your emergency fund.
I'm really not sure how you could live off $20K without a roomate or some other way of sharing expenses. Let's assume you take home $1,200 a month. Let's assume you find a DIRT CHEAP apartment for $500 a month. This leaves you $700. Electricity, gas, water, etc. would run you a MINIMUM of $100 a month and that assumes you don't use any A/C. If you have cable, internet, or phone service, that can run you another $100 to $200 a month. Now you are down to $600 or $500 dollars. If you eat Ramen noodles and cereal for every single meal, it would still cost you $50 to $50 a week.
How would you pay for transportation? Clothing? Gifts and holidays? Will you ever date? Eat out? Go to a movie?
If I were you, I would go to school and try to improve myself to where I could get a job paying at least double what you make now.