Ooooh, I love point questions!
1) Are spirits and ghosts the same thing?
Yes. Most who work with 'ghosts' typically call them 'spirits' out of respect, but I've heard of people who classify them differently, like a 'spirit' was once a human, a 'ghost' was once an animal, but that's personal preference and not a universal law. Most people on this site call all ghosts spirits, so treat them as the same thing. If you're unsure, go with spirit. [unless your personal views are different]
2) What do I banish them with?
Many things. It depends on a few factors. The most common is probably sage smudge, or sea salt water. Sage smudge is a bundle of dried sage you burn like incense but is thick enough you can hold it and waft the smoke throughout the house. Of course the key in any spell is energy and focus, but the magickal properties of sage can cleanse energy [specifically negative] and you can then protect the house/person/object and charge it with positive energy. Cleansing can also be used on energy build ups, so it's a good thing to look into. There are more complex rituals to actually banish a spirit, but majority of the time it's unnecessary.
3) Do they need to be banished?
Depends. Many people hear a noise and conclude an evil spirit wants to kill them. In reality, it could of been the house settling. If a spirit is in your home, they usually don't want to hurt you. Many spirits were human at one point, they could be lonely and want a place to stay for a little while. Some enter homes and decide they want to protect the people inside. It's best to try and talk to the spirit first, sometimes you can just ask them to leave and they will. If you've got a particularly stubborn spirit who's attacking people you should banish it, but in all my years living with spirits, I've never had to banish any. I had to make a protection charm for a friend because a spirit was mad at her, but I never had to banish anything. I do regular cleansings and that seems to do the job of keeping negative beings at bay.
4) Is there any other information that I need to know about?
Oh there's tons of stuff you should learn about but I don't have the time. I suggest studying before seeking out a spirit. Firstly, research the logical explanations of spiritual encounters to rule out anything natural. Many 'ghost sittings' are people's imaginations running wild because of a strange sound which could be explained if investigated. You should also look into cleansing and protection to be safe. I also suggest avoiding a Ouija Board, it's not evil but It's a spirit magnet when used correctly that can bring more trouble than it's worth. You should look into other forms of divination such as pendulum work, automatic writing, or skrying.