As a first suggestion, stop using w3schools as a reference point, particularly for relatively new CSS properties such as linear-gradient - the newer the property, the less likely it is that you’ll find what you’re looking for there. Try taking a look at the Mozilla Developer Network site instead, and pages such as these specifically:
Using the keywords, there are 8 directions, representing the corners and sides of a box, to top left - to top etc…
Or you may give any direction in degrees within the 360 degree range: 24deg
The % defines where between the start and end the colour is, 50% being half way, 25% one quarter etc. You may specify a % value beyond 100% to place a colour past the end point.
You may use other units to define the colour placement, such as px or em, but % is particularly useful in gradients.
Note that in your fiddle you are using the -webkit- prefix and no version without the prefix. This will cause the css to fail in the majority of browsers that do not require the prefix.