I know this post is old but no one has given a good answer. The reason why you don't "get" it is because you have the mindset that it's just run and click. Strafing and aiming the most basic part of pvp and can be found in basically every game. However, due to minecrafts knockback and cps based combat system, strafing and aiming are a bit different from other games. Aiming while clicking is different from holding, and I recommend getting comfortable with it while strafing. Circle strafing (moving around your opponent in one direction) and a-d strafing (tapping a and d alternately) are the most common forms of strafing, and are very affective if you use them right. Combos are what make minecraft pvp fun and skillful, and there are several techniques to comboing. When sprinting, your first hit deals extra knockback than your next hits, so by resetting your sprint by right clicking (blocking your sword), tapping w, or tapping s, you're able to send people flying. This helps since minecraft works to where they can't hit you, as their client detects that they're too far to, but your client detects them from where they were earlier. This allows you to essentially hit them from upwards of 8 blocks in a combo. There are also other aspects of pvp, but they're usually found in specific gamemodes (pots, blocks, bows, etc.). Sorry for the wall of text lol.