It's a loan from the Government to help with your study costs. To get a Student Loan you need to sign a legal contract with the Government, and you need to take out a new loan with each new study year.
No. You don't have to provide any security or guarantee for the loan, because the Government is providing the loan and will recover the money from you through Inland Revenue directly.
However, if you're under 18, you need to get your parent's consent.
There are 3 parts to a student loan plus a $50 administration fee for each loan account you use. You don't have to borrow for all three purposes.
Loan vs Allowance
What you borrow for living costs goes down by your Student Allowance.
Student Allowance after tax + Student loan living costs = $150.
For example, if your Student Allowance is $100 a week after tax, then you can only borrow up to $50 a week for your living costs.
Note that your Student Allowance is not a loan, you don't have to pay it back.
Once you earn over a certain amount a year (the 'repayment threshold' currently set at $18,148 before tax), you must start paying back your student loan, even if you're still studying.