How to Test Drive a Vehicle?any amount to pay or any eligibility or after test should buy it?

I'm confused about test driving,how will i test drive,simply walk to the showroom and ask them to give the vehicle for test,for that whether i have to submit amount for that and did they ask any eligibility for that,in bmw sites and all they asked about the previous car and all,so only according the position or salary or status they give the vehicle???????????????????