This song introduces lead-in notes, which are notes that occur at the beginning of a piece before the first complete bar of music. In the following example the lead-in notes are played on beats three and four of a count-in (as indicated).
You will notice that the final bar of the song contains only one half note (two counts), which acts as a "balance" to the lead-in notes. This is quite common, but does not always occur. Lead-in notes are also called pick-up notes.
The most famous Rock guitar amp of them all, the Marshall 100 watt amp with a 4x12 inch speaker "Quad box" has been widely used since it was invented by Jim Marshall in the 1960’s. The term "stack" means an amp sitting on top of a separate speaker box. Marshall amps produce great overdriven sounds which are perfect for both Rhythm and Lead Rock guitar.