Er, um, and uh are "hesitation devices" and they are extremely common in English.
People use them when they don't know what to say, or to indicate that they are thinking about what to say. You should learn to recognize them when you hear them and realize that they have no real meaning.
Example: I was wondering, ummm, if you would be interested in, uh, maybe, uh, going to the movies with me on Saturday.