Legitimate agents don't "charge" anything. If anyone, ANYONE, wants you to pay him or her for reading/submitting/publishing your manuscript, run, run, run as fast as you can in the other direction, and you might consider reporting him to Editors and Predators, as well.
Agents earn their keep by selling your work. Period. So if they make money only when YOU make money, which is critical, because their success is contingent on your success - this is why it behooves them to work for you. Agents usually take about 15% of the sale...so, if your ms sells for 10k, they earn $1500; if your ms sells for 100k, they earn 15k. You get the idea. Anyone who wants to charge you differently (more or less) is a scam artist. (I should note that these percentages might change slightly in the area of foreign rights, film, etc, but this is a general barometer.)
As far as how to get started? WRITE. Full stop. You cannot sell a book without having written it. I've read before that something like 90% of the populations believes that they are capable of writing a book. Ha! Of that 90% how many actually write it? Well, I don't have the specific percentage on that one, but I can assure you that it's a tiny fraction of this percentage. Wanting to write a book and actually doing it are two very, very different things. So get going. Prove to yourself that you're one of the few who CAN do it, not just dream it.