All of the melodies you have played so far involved a downward pick motion, indicated by t.
With the introduction of eighth notes, the technique of down and up (y) picking is used.
This is called alternate picking, and it is essential for the development of speed and accuracy.
In alternate picking, use a down pick on the beat (the number count) and an up pick off the beat (the "and" count). Try the following exercise:
The most famous of all combo amps is the Fender Twin Reverb. It produces a crisp, clean tone, even at high volumes, and is used for many different musical styles. Many players use a Fender Twin for their basic sound and combine it with effects pedals to add distortion and other effects.