How are the seats distributed in congress?

The Senate is easier to explain. It gives each state (50) 2 senate seats, so that totals 100 seats. In addition, the Vice President serves as the President of the Senate, but can only vote to break a tie. Thus it is called the Voice of the States.
The House of Representatives is more difficult. It is the voice of the people, so each state is, first of all, awarded House seats based on population. There is a given number of seats in the house, 435, which are distributed among the states. California, by far the largest in population, has the most house seats.
Within each state the seats are divided up based on population, so that, for example, say California with about 54 seats (approx.) would have their seats divided up, geographically, so that there would be 54 congressional districts with approximately the same population, each of these districts represented by 1 Congressmen (House member).
So, that , in the end their are 100 Senators (+1 Vice President) + 435 Representatives in the Congress for a total of 536 members of Congress.
Then these 536 Congressional members total the number of Electoral Votes in each national election for President, every 4 years.
A person to be elected president needs 50% + 1 of these electoral college votes, so the magic number to be elected President is 269 electoral votes every 4 years.