Route running is the most technical part of playing WR. There are so many routes with so many ways to run them depending on the coverage you get. Every receiver should have some type of plan before the play begins. Starting with the release if they are pressed.
There are many different ways to release but the important ones to master at first are the speed release, single move release, and double move release. Releases are only used against press coverage, if there is no press then stride it out.
The speed release is the easiest release in football. The best way to speed release is, at the start of the route, quickly getting your feet square then suddenly bursting past your defender. Very similar to a basketball hesitation move. This can be extremely effective if you know you're faster than your defender because it'll cause them to freeze and then you can leave them in the dust.
The single move release is the same as the speed release with an additional step. You're going to quickly get your feet square then suddenly jab inside or outside and release through opposite direction. It is important to use your head and shoulders to really sell the jab. Just like a basketball crossover without the ball.
The double move release is the same as the single move with another additional step. Same as the two previous releases, quickly get square, then jab inside or outside, and another jab to the opposite side and release through the opposite direction.