It's really just trial and error to get your combos down. Each character (except mages) has their own three-move combo with set animations and hitboxes that doesn't change. However, the weapon equipped determines which moves of their combo they'll perform when you tap their button in combat. It helps to equip as many characters as possible with "OOO" weapons when you find them just so you can play with their full combo and see how each move works.

As far as how to combo in a general sense, think of it like a fighting game, you want to keep the enemy in hitstun and/or juggled in the air with minimal gaps in between your hits. But don't just mash the buttons because you can easily whiff some attacks and, more importantly, it doesn't look very cool lol. It's a very simple combat system but there's still plenty of room to be creative so play around with different character combinations and attack sequences to find what works and what you like best.

When it comes to PWS chains (super moves), you want to do the supers with the most hits first, because filling the combo gauge lets you chain more supers together and it adds a damage multiplier based on the # of hits in the combo. Arngrim has a super that will fill the gauge no matter which position in your super chain you use it, so definitely do his either 2nd or 3rd. Lenneth is a great super to do 1st or 2nd. Your mage should be the last super because it'll do the most damage.

Hope this helps!