A good place to start is a book called "ABC's of reloading" its is a very helpfull book, I used that when i started reloading, and still referance it every now and then even now. Its explains everything you HAVE to know to start reloading safely. Including die parts description and to set properly set each kind up.
I am not throwing a punch or trying to be rude here, but if you are unsure of what die is what, and what part of the dies go where you shouldnt be reloading anything yet. Take it slow, otherwise you may hurt yourself or others with flawed rounds, or just load horrible rounds that wont hit a tank at 25m.
As everyone else is saying, there are many different kinds of die packages.
some 3 die kits are
decapper/sizing, expander, and seating/crimping die. ( this being how my 9mm dies are set up. )
Or
FL sizing and bullet seating die.
Then you can get into competition dies, which add micrometers and bushings, like my 338 lapua competition dies for example.
To go back to advise, start with an easy cartridge and work your way up. Maybe .308win, then work up to harder calibers. I think i started with .223 win and worked my way up to what i consider some of the harder rounds to load, 50 BMG and 5.7x28mm FN. 5.7 being a very finiky round to reload, the margine between min, and max powder loads are very small, not to mention to lack of reputable data.
but i digress, im rambling. To sum it up, hit the books. Then the press.
Tony.