What is a "Type?": Type Casting is essentially a method of categorizing performing artists based on a variety of factors. These factors include, but aren't limited to:
Physical Looks (Facial structure, hair color and style, build, height, etc.)
Movement (How do you hold yourself? How do you walk around? Do you walk with your head or your chest? do you slouch? Etc.)
Voice Tonality (Does your voice sound small, large, soft, hard, high pitched, low pitched, etc?)
There are a few factors to your type that can be changed and influenced, including your presentation style (Do you attack the words and command the scene like a Samuel L. Jackson? Or are you a Brooding and cunning Alan Rickman?), your physical movement (Do you shift your body into certain ways to fit a character? Would you slouch on purpose for an introverted character maybe?) and simple obvious things such as the way you dress (maybe you wear a suit or professional looking outfit if you are going for something more mature, or for the women if you wanted to play a more sensual character maybe you wear something to make you feel more sensual, etc.).
So how do you find out your own type? The best way is to ask people that don't necessarily know you very well. Ask professionals in particular. Your family and friends may not be the most honest with you, and because they personally know you, their perception is going to be different. Also, look at your resume itself. What is something each of these characters have in common, there are clues in there. Have you played a lot of similar roles? That is your type.
An actor that knows their type is going to be a step ahead of other actors. If you walk into the room and do something that isn't fitting right, the casting director may be distracted trying to imagine you as this completely different character. When a performer comes in and does something in their type, they will think "This actor is smart, they take advantage of their type and know what works for them. I want a smart actor like that in my cast."
Play to your type, and you will get more offers.
Break a leg!