Unless your home is quite old your plumbing pipes are copper or plastic. Plumbers used galvanised steel water pipes in early 20th century homes but gradually switched to copper because it is more sanitary and less prone to corrosion. Galvanised pipes were still part of outdoor plumbing in 2010. Early 21st century drain lines are of ABS or PVC plastic but the main stack that leads to the sewer is often cast iron. Each of these plumbing pipe types has a different method of connection.
Screw galvanised steel pipes together. Wrap plumbing tape clockwise around the threaded end of a pipe, insert it into a fitting, and turn it clockwise by hand until you can't turn it anymore. Finish tightening it with a pair of pipe wrenches. Hold the fitting with one wrench while you turn the pipe with the other.
Insert a union into a galvanised line anywhere you may need to separate the pipes in the future. It has two halves connected by a central locking nut.
Separate the halves and screw them to the pipes. Bring the pipes together and connect the union by tightening on the nut with a pipe wrench. You can separate the pipes whenever you need to by loosening and removing this nut.
Clean the end of a copper pipe that is to be joined with a wire brush to remove oxidised metal. This is prepartion for soldering, or sweating, the pipes. Spread flux on the end of the pipe and on the inside of the fitting which you want to connect to with the small brush that comes with the flux.
Insert the pipe into the fitting and heat the joint with a propane torch until the flux smokes.
Remove the heat and touch the end of a coil of lead-free solder to the joint. It will melt and wick in, fusing the pipe to the fitting.
Select the type of pipe cement for gluing ABS and PVC plastic pipes together. Each type of pipe has a specialised glue but you can buy a multipurpose variety that works on either.
Spread glue on the outside of the pipe and the inside of the fitting using the applicator that comes in the glue can.
Join the pipe to the fitting immediately. The glue will form a watertight seal in less than a minute.
Unscrew the nut from the fitting and remove the brass ring in preparation to joining copper tubes to copper water lines with compressions fittings. You will find the fittings are usually already installed on the tubes.
Slide the nut along the pipe with the threads facing you, then slide the ring onto the end of the pipe.
Fit the threaded end of the tube over the pipe, then slide the nut down and screw it onto the threads. Tighten it with a wrench.
Bolt cast iron waste stack pipes together. They are constructed with flanges with preformed holes for this purpose. Join copper to PVC pipes with threaded adaptors. Solder a copper adaptor to the copper pipe, then screw on the matching PVC adaptor. Glue the plastic pipe to the PVC adaptor. Connect copper to galvanised steel pipes with a dielectric union. It has a washer and insulator to keep the pipes from touching and corroding each other. Plastic P-trap assemblies for sink shower drains have compression fittings that you can tighten by hand.