US presidential election: do all citizens vote for the primaries, or only the members of the party ?

You are correct citizens vote for delegates in the primaries and any legal registered voter can vote you choose before you recieve your ballot wether you want to vote Democrat or Republican if you register Independent if you register Democrat or Republican you recieve that ballot I dont know why they dont just have everyone enrolled as an independant. The caucuses are the primaries in the individual states there is not one vote day for all states in the primaries it is divided over a period of months the general election which is held every 4 years in November all states vot on the same day.