Red notes are the most basic kind of notes in the game. All you simply have to do is to tap when it approaches the yellow line! Another thing to note about red notes is that there are yellow variants of the note which does not do anything special and only gives more points so be sure to tap it!
Sliders are also a very common type of note in the game, simply tap when the note approaches the yellow line and hold to the end of the note! Sliders also have a yellowish orange color and is the same as the yellow notes, it just gives more points
Air notes are a little more complicated, you may notice that on the sides of the machines that there is a thing that looks like a box with holes on the side, these are sensors and dectect when your hand is lifted up. For air notes simply lift your hand up and hold it there if you see a green line! if you see any purple notes like shown above and the ends or middle of green lines you have to move your hand in the air.