Tutorial on how to install bike pedals. Pedals will usually have left or right hand markings on them, either on the body of the pedal or on the end of the spindles.
Starting with right pedal, first make sure you grease the spindle and clean the inside of the crank arm threads. As you install it pedal backward and hold the pedals straight, and make sure the threads engage straight. The pedal should thread on smoothly, if it is not, stop immediately and try again. You do not want to cross thread the pedal. Once it snug, give it one more oomf. And don't say um so much.
The biggest thing to remember about installing pedals is that the left pedal is lefty tighty instead of the usual righty tighty we are trained to remember. Once you get the pedal started you can just hold the wrench onto it and rotate the pedals backward to make it quick.