As a beginner, your awareness has most likely revolved around shot making. You shoot at whatever you see, easy or difficult, and the cue ball rolls to wherever it goes, and you repeat the process.
More advanced players, however, are much more focused on positional play. They control where the cue ball goes, and so they shoot mainly easy shots. This is what allows them to break and run multiple racks in succession.
They control the cue ball by using spin. Top (Follow), bottom (Draw), and side (English). Follow and draw, involve hitting the cue ball on the vertical axis, and there is no alteration in the path of the cue ball.
English, involves striking the ball on the horizontal axis. Because the cue ball is spherical, when you hit the ball off center, the cue ball is sent on an altered path. This is commonly referred to as squirt or deflection*. Additionally, there is another phenomenon called swerve, which is a slight masse effect cause by the side spin that will cause another alteration in the path of the cue ball.
Essentially, when you use English, you may aim in one spot, and the cue ball will travel to another.
As a beginner, your primary concern should be developing a straight stroke. During this developmental phase, your mind inputs feedback from your all your shots and makes slight alterations and corrections.
If you begin using english, you will prolong the process of developing a straight stroke. This is because there will be usable data, and more confusing data for your mind to sort through. Eventually, when you actually want to hit a straight shot with no english, you will have much more confusion as to where you are actually aiming. It will be much more complicated then simply looking at your target and firing away.