At first you may only notice small changes, often to do with memory loss or impairment. Behavior and symptoms experienced by your friend or relative will change over time. All of us experience changes in mood, in the way we act and speak, that is normal. For someone with Alzheimers disease that will be true too, but their brain is damaged and that damage increases as time goes on.
Imagine yourself in a situation where you cannot remember your name, you are not sure if the person talking to you knows you, but is making you go to the bathroom. Imagine that you are not familiar with your surroundings - your behavior might also be a bit strange and you might be frightened. It would certainly be very confusing.