It is imperative to learn right from beginning that it is not possible to count the cards if you're playing an online game. Even if there is trick that you use for counting cards in a blackjack game or any of the card games, it won't be useful in online casinos because each of their deals are from a completely shuffled shoe or deck. Otherwise the online casinos will be actually giving away their money to the smar gamers. And everybody knows they wont let this happen. However, if you happen to be a keen gambler or someone who is just willing to know the tactics that the pros employs for beating the casinos, this brief summary will help you big time.

By means of counting the cards, you could ascertain whether you are having an edge on the house or not at any given time. To know if you've an edge on the house, it is important to get an idea that rest of the cards within the shoe or deck are high or low. Because, a higher card deck or shoe favors the player and you could be rest assured that you would have edge on the house.
So if you're already aware that the rest of the shor or deck is full of higher cards, then you must realize that you've got an edge against the house & for doing that you just ought to track those cards that have already got dealt. But there is nothing to worry for it does not necessarily mean memorizing each and every card which has got dealt, instead tracking those cards by means of assigning a sort of tag with the cards & then keeping a count of those tags.
The count prior to the very 1st deal is zero. As the cards get dealt, you just need to keep adding the tags for each card dealt such that during any point of time you get one running count which might be either positive, zero or negative.