presidential exploratory committees

So, what do presidential exploratory committees do? How many people are generally on one of these committees? This is assuming that actually do exist, and aren’t just a silly political catchphrase.

My experience with politicians doesn’t extend to the Presidential level, but I have a pretty good guess that the “exploratory committee” is the candidate and a couple of close associates calling up major contributors and asking

a) I want to run and I wanted your input and by the way
b) It costs a lot to get a campaign off the ground and how much would you like to contribute

From Project Vote Smart Presidential Campaign Definitions

The Libertarian party in 2000 put together a guide to the hurdles of mounting a presidential campaign and the role of the Federal Election Commission.

Simply, it all has to do with tracking where the money comes from and where it goes.