PokerTracker 4 complies with PokerStars terms of service and where necessary some functionality is limited when playing there such as the importing of observed hands and PokerStars rules on the coloring of HUD statistics.
Yes.Poker HUDs are legal and the majority of poker platforms allow HUDs on their side. HUDs track/record player information and process it to present in the form of numbers and percentages. Players use these numbers and percentages to know about their opponents' playing style.
Poker has a gambling element to it, which leads some players to question if poker is just down to luck. Although there is a serious amount of luck involved in poker, the fact the same big names regularly win in cash games and tournaments shows that there is skill involved.
Playing online poker for real money is risky, but there are a couple of things you can do to minimize risk and maximize your winnings. Bankroll management, table selection, playing tight aggressive poker, avoiding multi-tabling.