Basically: Each state has a certain amount of Electoral College representatives. The amount is based on the amount of representatives that state has in congress (which is based on population size). So California has 2 senators and 53 house seats, which means they have 55 Electoral representatives.
Each state will hold a popular vote for the presidency, and the electoral college casts their vote based on that. The electoral college basically always agrees with the popular vote (except in Maine and Nebraska). If a candidate won the popular vote in California, that would mean that candidate gets 55 actual votes (from the electoral College). The number of electoral representatives is different for each state. For example, Kansas only has 6.
\*This is an indirect method of electing the president by reaching the final tally in the College.
For a more detailed explanation: Handbook p.177