What the heck is a 'Collectable card game'?
A recent addition to the world of games, CCG (Collectable Card Games) started in 1993 with Richard Garfield creating a game called 'Magic the Gathering' (MtG).
A CCG is not purchased all at the one time, in fact you may never have the whole game.
A classic example of CCG's is 'Magic the Gathering' so I'll use it as an example. There are currently about 17,500 differant 'Magic' cards available, and your objective is to choose 60 of them and use them in a deck to defeat your opponent. Most players of the game have anywhere from 1,000 cards to 10,000 (as a trader I'm sitting on about 60,000 - yet I know players that have more than that!).
To use an analogy - imagine playing poker but only having a quarter of the deck, and your opponent only has a quarter of the deck as well, but neither of you know which cards are in your opponents deck let alone their hand!
As you can expect, with 17,500 cards available not all cards are created equal - in fact, some cards are useless by themselves (imagine the 2 of hearts, a weak card in Poker - but put it with the 3,4,5 & 6 of Hearts and it's very powerful!), while others are very strong (an Ace is always a good start in Poker).
So you really need to work out which cards you would like to play with, that's where practice/research comes in; if the game was made correctly then there is no one answer to which are the best cards to use; currently in tournaments there are about 700 cards that are used.
The most important thing about these games is to have fun; and with so many cards in the game there is very little chance that your opponent has seen them all, but also be prepared to see cards in the middle of the game that you also haven't seen!