Random number generator with random seed (gfortan)

I use gfortran for a simulation. I want to random generate a number and give the value to variable of a particle. I have to do this process for 1000 particles, but i don't want the same random value for all of them. So i am trying to use the function RANDOM_SEED in combination with the function RANDOM_NUMBER. I want the seed of RANDOM_NUMBER to be different in each loop, but i don't understand the proper use of the RANDOM_SEED function and how to achieve that. It could be very useful if someone could provide a script with the solution.