lot size in order book

Hello friends

I have some very basic question.(since I am new, Pls forgive me to ask such a ?)

1.How to enter lot size while ordering in F and O?
I know for nifty one lot is 50. whether one has to enter 1 or 50?

2.Likewise BataIndia one lot is 500 shares. while placing order one has to enter 1 or 500.
Is it remain same for all trading software?

I saw one post, where one member in currency option while placing order entered as 1000 instead of one.

I need to clear my confusion. Dear seniors kindly clarify.

Regards