sampling and frequency shift

I am generating a pulse signal with a very high freq and a long code length.

what i want to do is firstly to oversample this pulse signal (discrete signal) and see how this sampling will look like in frequency domain. my teacher said i can also use interp function for sampling the signal or upsample, but i still didnt get the difference between both.

then, i want to frequency shift this sampled signal by factor of 2e9, so i was thinking to multiply the signal by exp(-i*2*pi*2e9*t)

i would be grateful if someone can help me with this, since i am still confused about this.