Conduit comes in many styles and is used to run electrical wiring in exposed locations in and around your home. It may be a basement, garage, barn, laundry areas, and also exposed areas. Your home may have conduit run inside of the walls, giving you access to pull additional circuits through the existing conduit runs later on.
Stranded or solid wire is usually pulled through conduit and is usually either THHN or THWN type wire. The size of the wire may vary, depending on the amount of amperage needed to supply the point you are feeding, and this ultimately determines the size of the conduit that you will need to install.
Conduit that is installed outdoors must be rated for exterior use. PVC conduit is often used in underground and wet location applications. This type of conduit has its own PVC fittings, connectors, couplings, and elbows. They are easy to attach to one another with a cleaner and PVC glue. Since PVC conduit is not conductive, you should always run a green ground wire in the conduit for proper grounding methods at connection points.
Flexible metal conduit is great for aeras that require tight bends and close quarters would make it difficut to bend regular conduit. Water heaters, can lights, and attic vents are great examples of typical flexible conduit installation.
EMT conduit is lightweight, easy to bend, and is use within the walls. It also is easily damaged, unlike IMC or rigid conduit.
IMC conduit is a thicker conduit that is galvanized, making it a great choice for outdoor installations. This is also a good choice for exposed walls in basements, garages, outbuildings, and areas the conduit can be hit or damaged.
Rigid metal conduit is the thickest and heaviest of all. It can be used to run wires under driveways, service feeder installations, and other more extreme condition areas. Rigid conduit must be threaded on the end and is more expensive than the other conduits listed.
All the above mentioned conduit types have a maximum allowable fill percentage.