1: Start with an easy character, just one of them. Patroklos is great for running up and pressuring people, Mitsurugi is the master of the 50/50 gamble, Pyrrha is safe & fast with good punishment, Aeon is mediocre at everything but superb at spacing and the undisputed king of ring outs in this game. Any of them would be great starter characters, other characters with similar Ease of Use stats require greater compensation for their flaws(like Nightmare being the most punishable character or Leixia dealing dangerously low damage).
2: Advantage! If you land an attack or block an attack, you're at advantage and the opponent is at disadvantage. Your next action will be faster and their next action will be slower. To avoid extra damage, most of the time you want to be blocking when you find yourself at disadvantage. Missing an attack completely(whiffing) puts a player at a quite a bit of disadvantage and usually means they can't block in time to avoid being hit if their foe capitalizes on it. Some attacks have a lightning effect on them, these break guard and leave the victim vulnerable briefly: in some cases even guaranteeing certain attacks. There are also certain slow, powerful attacks that place their user at advantage any time they hit, but these are few and far between. The thing to remember about advantage/disadvantage is that it goes away almost as soon as it comes: if you don't take advantage of it immediately it's lost and you return to neutral.
3: Spacing and movement. Spacing is, in short trying to maintain an ideal distance from your foe to make it difficult for them to even touch you for longer-ranged characters or ensuring that they can't safely move away for shorter-ranged characters. This is best accomplished by moving a lot and memorizing how far your own attacks reach out to. But movement itself has risks involved: forward movement puts you more in harms way, any other kind of movement has a cooldown on blocking(about a third of a second) and being hit while moving in any direction but forward makes you eat full counterhit damage instead of normal damage. This is something to exploit obviously, make your foe want to move and smack them out of their movement. Which is easier to accomplish when you're spacing well :)
4: Punishment. Punishment is exploiting your foes mistakes for guaranteed damage that can only be missed if you mess up your input. Most punishment comes from stepping to cause whiffs and blocking unsafe attacks. Every attack has a certain degree of 'safety' in how much disadvantage it places the user when it doesn't land how they intended. In some cases this means you can launch them into a juggle combo for a lot of damage, sometimes you'll only be able to get in a basic poke. Regardless, you should try to punish everything you can: it's free damage and your foe is literally defenseless against it unless they somehow don't make any mistakes.
5: Timing, mixups, and mindgames. Changing your timing on things is another great way to get free damage. If you seem to keep getting smacked out of your attacks, try just standing there and blocking until your foe takes the iniative, figuring out how long they like to defend before attacking, and then smacking them out of their attacks! If you keep changing up your timing you can make your foe more cautious and have an easier time forcing a mixup on them! A mixup is pretty much just like it sounds: mixing up your opponent by doing different attacks. All characters have access to the basic low/mid/throw mixup at close range, most characters have many additional mixups either with stances, delayable attacks, or the like. The goal is to make your foe expect one thing and do something completely different so they can't defend themselves. Which is a great mindgame! Mindgames are pretty much *THE* thing in Soulcalibur. You can do something weird to confuse an opponent, like drop a launch combo early to hit them with an unblockable attack as they get up, cancel a cancelable attack, do a non-ring out throw in a situation a ring out throw would work to avoid getting your thrown broken...Get them out of their comfort zone and make them suffer for it.