I have one 7.4 V battery, one 6 V servo and an Arduino duo.
what are the necessary components that I need to add to make the servos work?
Do I need to add some voltage regulators? or
Do I need to add some capacitors/resistors?
if I need to add more components please tell me where I should connect them.
If possible please provide schematics.
thanks!
an Arduino duo.
A what?
Arduino has a Uno and Due. I guess you have one of them?
But it sounds like you probably just need a 6V DC-DC converter and some wires...oh and a program of course.
Steve
Maybe your best bet would be to start by looking at some easier example projects and trying them out!
Take a look here for example: 15 Great Arduino Projects for Beginners
You can find many more examples to study if you search the internet for "Arduino example projects".
You're going to be learning a lot of new things! Enjoy the adventure 
I have one 7.4 V battery, one 6 V servo
Do you have a data sheet for the servo. Many servos are specified to be able to work with 7.2V. The data sheet will tell you what the rated voltages are. If you don't have a data sheet, post the brand and part number of the servo and we can help you find a data sheet or maybe someone knows.
You can power an Arduino UNO direct from the battery . You can put two diodes in series with the supply to the servo , which will drop you 1.2 volts.
Don’t power the servo from the Arduino