akram there is something called a day rate on your contract
when you have something on a day rate. You get paid for only the days that you work.

For example if you have like a day rate of 100$ per day
at the end of the month u get 2600$ why is because friday is not paid.

if you work on an off day you get paid over time which is normally 1.5 times more than the normal day rate .
so say you work on a friday you get 150$

however if you have a monthly salary. it is considered as all inclusive.
so you take an off or you dont
you go on leave or you dont
you will get paid a fixed salary

Check the contract mate its easy and simple.