The usage of randomstate in Numpy related to seed

I'm working on deep learning lately. During the studying several python scripts, I found this line.

numpy_rng = numpy.random.RandomState(123)

I believe this RandomState generates random numbers for bias and weights for machine learning.

But I have no idea when it comes to that '123' numbers which called 'seed'.

I would like to know what exactly seed does.

Can I just write any number I like? totally it's up to me?

One more, is there a way that I can print the random numbers that were generated by RandomState?