Apologies way in advance because I know these questions have all been answered before, and if you'd like to just direct me to the answers that'd be fine. Also, yelling at me for not being able to search properly is fine too, I can take it. Although I can assure you I tried.
First three are related.
1)
I cast detect magic out of sight, out in a hallway. I walk into a room. Do the people in the room know that I'm currently "detecting magic" without having seen me cast the spell?
2)
Detect evil, same question.
3)
I'm a paladin, and use my detect evil ability. Same question.
4)
I'm speaking to someone and in the course of the conversation I throw Charm Person. Do they know that I'm casting a spell at them as I cast it, and therefore are they immediately hostile to me because of the spell being cast on them?
1.No, but since the spell requires concentration they should be able to tell something is up.
2 and 3. See 1
4. They know you are casting, but unless they have ranks in spellcraft they don't know what it is. They don't know the spell is cast on them until it affects them, and in the case of spells calling for will saves they sense a hostile force. If they fail the save you have a new friend.