U shouldn't be really questioning yourself on which way to shoot....just go with your first instinct. If the first time u ever old a hockey stick at a shop when u go stick shopping and your left arm is on the butt end and ur right is on the shaft...ur a right hander. Vice versa the opposite way.
As for slapshots, power will be driven from the upper body strength.....then the follow through of your shaft arm......then the torque from your stick. So practice whats needed first, which is making sure ur arms find a perfect position. If the shaft arm is too high, u will golf swing with no power....too low, then you won't have proper balance to execute. Find a perfect position for the puck...work on your stance and balance first,....so that means you shouldn't practice doing slapshots by skating up to a shot; do stationary shots.
Thats pretty much the beginners part of it.......Berz was pointing out the flex of the stick. However, in my opinion, using the flex of a stick on a shot or slapshot is a difficult skill, but an awesome skill. After how many years, i have been playing, i still haven't figured out how to use the flex, so i don't use flexy sticks anymore. I'm sure other RS'ers are gonna say its easy to do
but hey....you're learning. Get the basic steps down packed, and the rest will come by experience.