What are periods in pseudo random number generator?

I am reading a text from a book. But since pseudo random number generation is a complex topic, I just was expecting a very basic answer for beginniers. What is the signifigance of period in pseudo number generators. Why is a higher period better? Also what are states? Is having more states better?

Of the three pseudo-random number engines, the Mersenne twister generates the highest quality of random numbers. The period of a Mersenne twister depends on an algorithmic parameter but is much bigger than the period of a linear congruential engine. The memory required to store the state of a Mersenne twister also depends on its parameters but is much larger than the single integer state of the linear congruential engine. For example, the predefined Mersenne twister mt19937 has a period of 2^19937−1, while the state contains 625 integers or 2.5 kilobytes. It is also one of the fastest engines.