One side screws on clockwise the other side screws on anticlockwise. Tighten with spanner or allen key depending on pedals.No extra bit required!(sorry).
Make sure threads are clean, grease threads well. Tighten driveside pedal clockwise and non-drive side anti clockwise (LH thread). You will need a 15mm spindle or on some high end pedals a 6mm or 8mm Allen (hex) key that inserts from the reverse of the pedal spindle (ie 'inside' the crank).
An easy way to remember the thread direction is to hold the pedal against the crank and turn the crank backwards to do it up. That does assume you've got the correct pedal for the crank.
Do you need to put pedals on with high torque? Or are the large pedal spanners needed for removal rather than fitting as they tighten due to pedalling action?
Explain the problem your having
there are 2 sizes of thread,1 for normals 1 for bmx[i think]
If you have the right size ,apply a little grease to the threads,thread in using your fingers,then tighten a little with a !5mm spanner,you only need to tighten a little,dont horse it on with maxed out torque,lest you shag the threads on the crank
Ive never had a pedal unscrew on me