UDF file

Hi

I am the new user of COMSOL simulation.
I want to simulate fluid flow with velocity is function of time as below:
V = 0.1m/sec for 0<= t <=5 msec
V = 0 m/sec for 6 <= t <=200msec
Can anyone help me how to write that function in COMSOL? I have written it in udf file but I don't know how to import udf file into COMSOL.
Please help,.....