All the examples you have played so far have involved a downward pick motion, indicated by a a. When playing eighth notes, a down (a) and up (s ) picking technique is commonly used.
This is called alternate picking, and is essential for the development of speed and accuracy. The technique involves using a down pick on the beat (the number count) and an up pick off the beat (the "and" count). Practice example 10 using alternate picking until you can do it comfortably and then try example 11.
Here are some more examples to help you become comfortable using eighth notes. Remember to use alternate picking and count out loud as you play along with your metronome. Practice each one slowly until you can play it smoothly and evenly and with more confidence.