The "seasoning" on cast iron is the smooth patina that builds up over time in the pan, creating a non-stick surface. The simplest way to season your pan is simply...to use it. Every time you cook with oil or fat, some of it seeps into the pores of the pan, slowly building up layer by layer, making the surface grow darker and slicker with time. But if you don't have the patience (or time) to take the long road to seasoning, it's also possible to get a jump start on the process using the oven. The internet is full of guides to oven-based cast iron seasoning methods; if you're going that route, here is one that's particularly thorough and reliable.
Washing and Cleaning
You've probably heard a lot of nevers when it comes to cast iron cleaning. Never use soap. Never use water. Never use a scrubber. But, relax: it's not that complicated. In general, the best way to approach cleaning cast iron is to start with the gentlest possible method—after all, you don't want to damage that lovely seasoning you've spent so long building up. For many simple dishes, that may mean simply wiping out grease and stray bits with a slightly damp paper towel. If more vigorous cleaning is needed, a rinse in warm water with a drop of dish soap should do the trick. For stuck-on crusts and bigger messes, add a tablespoon or two of salt into the pan with a drizzle of water and combine them to make a paste. Then use a soft sponge to gently scrub before rinsing all the residue and crumbs out. Just don't leave the pan to soak—a surefire recipe for rust—and make sure to dry it thoroughly and rub it down with a light layer of oil (canola is fine) once it's clean.
Moisture is cast iron's enemy, so make sure your pan is completely dried of water after you wash it and, if possible, it's best to store—or hang—pans in a relatively cool, dry place. If you're storing pans stacked inside a cabinet, you can also add another layer of protection by placing a sheet of paper towel between each one. This will not only prevent scratches and damage to the surface of the pan, but also absorb any liquid you might have missed.