Prerequisites

Physical

You don't have to be huge to play in net. I stand 5'10" tall and weigh only 125 pounds, yet I do fairly well. In my league there's a goalie who stands about 5'4" tall. Being small and quick is probably better than being huge and slow. But don't fool yourself: Hockey is a tough sport. It requires flexibility, speed, and stamina.

Mental

You need to be basically smart, able to learn by watching and by doing, and able to concentrate on the puck despite distractions such as noisy spectators.

Emotional

You need to be able to recover from your mistakes and not let them depress you or make you lose your temper.

Photo Copyright © 1998 by Michael Roeder

Equipment

Hockey is a fairly expensive sport, both for buying equipment and for ice time. Goalie equipment is even more expensive. Whatever you spend, get gear that fits you well.
Here's a typical list: jock strap & cup, compression shorts, goalie jock, socks, garter belt, stockings, pants, skates, leg pads, goalie collar, chest & arm pads, mouth guard, helmet, catcher, blocker, stick.
The web site Hockey Goalie Equipment has pictures and more details of all the gear you will need.

Basic Skills

For hockey players, the fundamentals are skating, puck-handling, and shooting. For hockey goalies the fundamentals are stance, movement, and angles.

Stance—Ready Position

Stand with your feet just wider than shoulder width apart. Bend your knees and bring them forward and together while bringing your butt straight down. Plant your weight on the inside edges of your skates; let your ankles bend. in this position you are well balanced. From this position you can quickly and surely move sideways.
Hold your hands out in front of you. Hold your catcher in front and to the outside so that its palm faces forward. You should be able to see it out of the corner of your eye. Because you can see your catch glove, you can move it to catch the puck. Hold your stick in a vertical plane in front of you about 8" away from your skates. The middle of the blade should be halfway in between your feet. Keep the blade on the ice at all times. Your coach or another player should be able to pass his stick between your gloves and your leg pads.
The Ready Position is stable and comfortable. It provides maximum coverage of the net and lets you move to catch, block, or otherwise deflect the puck. From the Ready Position flow all other movements.

Movement

You need to be able to skate better than anyone else on your team. Not necessarily faster, but with greater stability and skill. Centers and Wings only need to know how to skate forwards. Defenders also need to be able to skate backwards. Goalies, however, need to be able to skate forwards, backwards and sideways. The more natural your skating skills, the better goalie you will become.
To skate sideways, slightly pick up the leading foot and push away on the trailing foot, which is planted in the ice. transfer your weight to your leading foot and bring your trailing foot close to you. Throughout the shuffle, place your leading foot vertically so both edges contact the ice equally. The wider blade and shallower cut of the goalie skate will let you glide sideways.

Angles

Your primary way of stopping the puck from getting into the net is to place yourself between the puck and the net. You can see the semicircular goal crease in front of the goal. Imagine a line from the center of the goal net to the puck. Your job is to face the puck while staying on that line where it intersects the goal crease.
The hard part of being a goalie is to stop the other half of the shots.

Styles

Stand-up

Ready stance is feet together, with an emphasis on staying on your feet and using the stick and skates for shots on the ice. The signature move is skating the foot out to block the shot with the inside surface of the skate.

Butterfly

Ready stance is feet shoulder width apart, knees together. The signature move is to drop to the knees with the feet splayed out, pads facing forward on the ice.

Hybrid

Ready stance is stace the same as butterfly: feet shoulder width apart, knees together. Emphasis is the same as stand-up: staying on the feet to maintain mobility and using the stick for shots on the ice in the middle. The signature move is a half-V for shots on the ice to either side.

Advanced Skills

You cannot become a goalie just by reading a web site. You have to go out and play, attend goalie schools and camps, and practice what you learn. And then, when you’ve learned a lot, youneed to practice more.

Conclusion

To play hockey in the net, you need a solid foundation in stance, movement, and positioning. You need to learn from your mistakes while concentrating on the puck throughout the game. You need to control your anxiety and worry, pay attention to what your body is telling you, watch and interpret the play in front of you, react quickly, and make the right moves.