Is it necessary to deduct Tax at source even if one is employed for a short duration?

Is it necessary to deduct Tax at source even if one is employed for a short duration as low as one month.His salary works out to 25,000/- but was employed only for 45 days on a consultation basis.The company employed him has deducted a tax at 10 % of the total salary/compensation paid to him. The company can issue a certificate to the effect of deducting Tax. But is it correct in the situation his total salary drawn over the financial year in any case does not exceed the taxable income.

How much amount is deducted (at source maybe) as a contribution towards provident fund??

As you’ll would have guessed, I really don’t know a lot about salary deductions and contributions. I will really appreciate if someone can enlighten with the way the salary works in India? what sections/heading are people paid under? Which of those fields are taxable? How much gets deducted at source and for what reason? What exactly is a provident fund or public provident fund? How much tax is deducted under professional tax?

:o)