Hey there!
AR and DR are modifiers added by items and effects. As you can see on the Warrior, their armor and shield has a DR rating. There are no starting weapons that offer an AR bonus, so you’ll need to grab magic items to increase them.
In the testing I did, adding AR for starting characters made encounters a bit too easy whereas adding DR made it so they could at least survive a bit better if bad rolls came up. With more folks having more hands on the rules we’ll see if that logic holds up!
Let me know if there are further questions!