Although there were a few items in the previous games, Mega Man 5 has a whole set of them so let's find those letters and unlock Beat.
Gravity Man 1st M
You'll see the letter on your way through the stage. To snag it, quickly tap the jump button right from the ledge when you're upside-down so you cross the down gravity stream above the M then you'll acquire it once gravity reverses. It's much simpler than it sounds. v1d30chumz 107-21-85-250
Wave Man E
During the segment where you're riding a watercraft, stick to the left side so you can see the letter approaching after a couple of fish leap into the scene then time your jump so you can grab it.
Stone Man G
This letter is hidden in a room that's accessible after breaking a wall segment. When you reach a room that has a couple of ladders, a Metall, and 2 search mines; shoot the bottom-right wall then slide through the gap to find the G.
Gyro Man 1st A
In the segment with bridges made of falling blocks, you'll see the A underneath one of the blocks. Keep running right while jumping to dodge the spiky enemies then when you're over the letter, stand still and jump to the right as soon as the block falls and you'll hopefully collect your 1st A. It can be a bit tricky to time your jump but you could always just fall and sacrifice a life if you want to make it easier.
Star Man 2nd M
After progressing a little through the level, you'll see the M near the ceiling below some spikes so hold the jump button just enough to grab it without smacking your head on the spikes. It might take a few tries but you can do it! 😊
Charge Man 2nd A
Soon into the stage, you'll see the A in a window so deploy Rush Coil, hop on his back, and then jump at Rush's peak to reach it.
Napalm Man N
This is perhaps the most obvious letter to collect. Once you see it, just fall down while holding left to grab the N from the alcove.
Crystal Man V
At the part near the end of the level where you fall down a shaft that has spikes on the sides, keep holding left against the wall next to the hole within the first spike screen then advance to the next screen with left held and you'll grab the letter after the transition.
What does Beat actually do?
Beat is Mega Man's bird and you can use him by choosing Beat on the weapon select screen. While he's deployed, the gameplay remains intact except there are 2 differences. First, you cannot charge your Mega Buster which is kind of annoying. Second, Beat will automatically fly to and attack the nearest onscreen enemy which depletes some of his energy. However, you can recharge his gauge with regular weapon energy pick-ups as well as fully replete it whenever you collect a letter which is cool, I guess. Anyway, the 4 Dark Man bosses as well as Wily Capsule 2 are weak against Beat and that's where this bird really starts to sing! 🎵