You can simply add the pellets to the primary or secondary (for a pale ale I would consider not doing a secondary, it is not needed and will lengthen the time between fermenter and serving not to mention needlessly raise the risk of potential oxidation or secondary infection). The hops will fall out in a few days. If you decide to go with the primary route wait until fermentation has significantly slowed and the krausen has mostly fallen, then add your hops and let sit another 7-14 days at room temp.
The amount of hops is entirely up to you - but I find that for lower gravity pale ales I like to keep the dry hopping levels on the lower side, .5 - 1 oz per 5 gallons. For English hops I thing that .5 oz per 5 gallons is plenty, for American hops I will go a little higher. But ultimately it will be up to your personal preferences.
Also, if you are kegging you can add the hops in a muslin or nylon bag directly to the keg. This is the best solution because you can start out with a restrained hand and add more if needed.