Most people who will play Mega Man 5 probably have access to the previous titles in the series, and are likely quite familiar with the general process. However, there are a few changes this time around, so it's worth a quick refresher.
As usual, there are eight initial stages, each with a robot master waiting at the end. You can tackle those stages in any order, and visit them multiple times if necessary. When you defeat a robot, you gain his special power, which you bring with you to the other stages and can use against the remaining baddies. You also gain a password, so you can return to the game at a later date without losing your progress.
Rush has changed substantially. He's no longer a robotic canine. Instead, he takes the form of a power suit, which you can equip to destroy large blocks, or to briefly take flight. You'll gain those upgrades by defeating Flame Man and Plant Man. They no longer drain a meter, which is nice, but their use is also quite limited.
Beat, who debuted in Mega Man 5, makes his return. Finding him this time around works a bit differently, however. Instead of collecting obviously placed letters, you'll need to find hidden passageways in several stages. The trick is that a robot master is at the end of both potential routes through a stage, so you'll want to make sure you find the genuine article. Otherwise, you'll win an epic battle and miss out on part of your reward.
Controls are the same as ever. You run, jump and shoot, climb and descend ladders, and slide (accomplished by holding Down on the d-pad while you jump). You can also charge up your shots. A charged shot is powerful enough that special weapons can usually be saved for boss encounters, but even a properly powered up arm cannon blast doesn't feel as powerful as it did in Mega Man 5. You'll definitely want to equip the right weapons when you face off against the bosses.
That should be enough information to get you off and running. Let's get to work!