There is a variety of way to earn money online playing games, some you can do with no deposit or risk. Some sites are designed to pay the players, others are ok if you find a way to make some money and some it's against the ToS and could result in account loss. This section will help you determine all those things and provide links where applicable to help you along the way.
Skill gaming is usually played in one of four ways:
1. Puzzle games where logic and math skills play the biggest factors. Like Bejeweled and Connect Four
2. Arcade games are usually puzzle based but require equally quick reflexes with the mouse and/or keyboard. Like Pac-man, Billiards and mini-golf.
3. Word games testing your spelling. Like Scrabble.
4. Quiz games testing your knowledge about a particular topic area.
When you give a game a time limit like most arcade games, along with in game bonuses and such. You can make a nice score table for people to play against each other, that is based on skill. Since you can make sure both/all people playing that game for money play that same exact game with same conditions, this isn't considered gambling by the USA and Paypal.
Most of the time Skill gaming is a simple head to head competition. You both risk 50cents for example. Winner is the person who scores higher in that game, and they win 90cents. Most skill Gaming sites take a 10% cut for hosting everything. There is larger tourneys where everyone risks same amount and then the top few scores get a prize.