Infielders in baseball and softball share one trait all around the horn. They all have good soft hands and quick reflexes.
Why soft hands and quick reflexes? Because fielding ground balls is one of the toughest things to master. Even the best commit errors all the time, because the ball is very rarely simply rolling. It's always bouncing off something or has a strange spin off the bat.
The best minimize those errors with preparation and staying alert. Where fielders play are on the infield usually is dictated by arm strength. Stronger arms are at shortstop (between second and third) and third base, where the throws are longer and and need to come in harder. Shortstops have the toughest job, and likely the most active one. Second basemen have their own skill sets for turning double plays, but don't need the super-strong arm. And first basemen need to be the best at catching the ball, scooping low throws and leaping for high ones.
Left-handers can play first base, but infield play at second, third and shortstop is easier for right-handers. Why? It's simply easier for a right-hander to make the throws, because lefties would have to pivot in an odd direction to make the plays. It's not a conspiracy: There is not a single left-hander at any of those positions in professional baseball.
There's a lot more to playing the infield than catching the ball, of course. There's cutoff throws from the outfield, who covers which base in which position, etc. But for the basics on grounders, here's a step-by-step look.