Difference is the change between things..
not manners as below...
Being polite and kind is good, it shows you are polite and well bred. That you care about your fellow people and don't want to offend them. Customs for addressing royalty, your fellow persons and so on are just customs - way to make being polite easier.
Don't worry about getting it wrong, so long as you do it in a polite and considerate manner. If you don't know the correct form of address, it's fine to call everyone "my lord" or "my lady" even if they are also eligible for a higher title. Rude is "hey you" or "you slob in the high throne" (unless you KNOW the person, AND everyone else in earshot WILL take it as a joke).
It is useful to remember that the Middle Ages featured an armed society. Armed societies traditionally are very polite, for relatively obvious reasons. In the SCA that most uncommon of things, "common courtesy" is celebrated. You get the chance to revel in holding doors open for people, helping someone who is obviously having difficulty with a heavy box, assisting total strangers with setting up their pavilion and treating all and sundry with the grace and courtesy you wish you could experience every day (especially in peak hour traffic!). Feel free to bow or curtsey, to greet in flowery language, or to flatter and praise, because the SCA is the one place where you should be able to expect the same treatment back.