Undestanding timers

How can I generate three pulses with 120 degree phase shift and 10KHz frequency using arduino UNO R3?

How exactly is that related to the timers you mentioned in the subject? The UNO doesn't have a DAC, so without additional hardware you cannot produce waves. Maybe you should describe in more detail what you're trying to achieve.

You need to figure out how many clock cycles it takes for your period, set a timer interrupt once that period is up, and then change your output within the interrupt. How long are the pulses to be?

gayathrisankar:
How can I generate three pulses with 120 degree phase shift and 10KHz frequency using arduino UNO R3?

How long are the three pulses? Are they all on one pin or on three different pins?

Probably, the OP is trying to generate 3-phase balanced signals for 3-phase DC-to-AC Converter. Therefore, the signals should be on 3 separate pins and synchronized. In the good old days, we were creating these signals using 8085 MPU/89S52 MCU and 8253 Timers.
3phaseTime.png

Generation of the above synchronized and 1200 phase-shifted timing signals would be an interesting exercise.

3phaseTime.png

gayathrisankar:
How can I generate three pulses with 120 degree phase shift and 10KHz frequency using arduino UNO R3?

What are you actually trying to do?