If you want to fly, first get elytra wings. You can find elytra wings in floating ships in The End and you can repair it with phantom menbranes. Kill phantoms to get it. Next you will need fireworks that don't blow up(so you do not die from the fireworks).

First get paper from suger caine and then kill creepers to get gunpowder. Put paper on the crating tabble an then gunpowder. 1 piece of gunpowder goes low 2 pieces gets you a little high and 3 pieces goes very high when your in the air.

Now wear your elytra wings and hold your fireworks(I recommed you put the fireworks in your off hand so you can use other stuff while flying unless your on bedrock). Next jump from a highish place and jump in midair then click your fireworks now keep clicking to stay in the air.