Online blackjack rules are the same as if you were playing in a physical casino. Just because you are sitting comfortably at home or work in front of your computer does not mean that the rules are going to be different. Blackjack is blackjack: the rules are simple and consistent.
Learning Online Blackjack Rules
Since online blackjack rules are the same as any other place where you can gamble on blackjack, most people will know how to play. But, if you don't know how to play in the first place, you should get a tutorial or have someone with experience give you some tips.
The object is to get as close to 21 as you can without going over. If you get an ace and a card with the value of 10 off the deal, it is a blackjack. If not, you have the ability to hit until your cards equal a number that you are hitting on. If you go over 21, you bust and lose automatically, no matter what the dealer has.
Knowing the rules is generally not enough to be an effective player. Anyone who is going to put their money on the line should also know the basics of the game. This includes simple strategies like when to hit and when not to hit. Different people are obviously going to give different advice, but the common unspoken rules should be known and followed by everyone.