Have several cashier

i several cashiers , so how can i install sambaPOS with the same license and the same databases on them all?
should i also buy license for every one?

You mean several terminals/tills?
You only need one licence.
You will need to use SQL Express for multi terminal.
Put SQL Express on the best spec terminal and install samba and set connection string to the SQL express install.

Go to kb.sambapos.com look at the setup section.

Hi the following link may be useful,

2.1.6. How to Run SambaPOS on Multiple Computers?