Chairs should be made of a hard wood that can support a lot of weight and withstand many years of use. Oak, pine and cherry are popular options. You will need a one inch thick piece for building the seat. Cut the seat to your desired dimension. Most kitchen chairs have a seat that measures 18×24 inches.
For the legs, you can use pre-cut spindles, or build your own. Use a 2×2 inch board and cut your front two legs exactly the same length, about 18 inches long is standard. Cut the back two legs 4 feet long. These two legs will also double as support for the back of the chair. You can turn the legs on a lathe to round them out and create decorative variations in the wood before you start to assemble. Alternately, you can purchase a thick hardwood dowel and use it for the legs of the chair if you wish.
Take the seat and attach the front two legs. You can chisel out a slot for each leg on the underside of the seat if you wish. Create a dowel joint to securely hold the legs in place while avoiding the need for screws and nails on the seat surface.
Now you will need to chisel out a slot for the seat on the back legs. Use a hammer and chisel or a router if you have one. Make a slot that goes about one-half inch deep into the legs and that starts at the exact length of the front two legs. Measure and visually test the height of your channel on a flat surface using a level before you cut. Test the seat to make sure it fits securely into the slot. When you assemble the seat and back legs, you may want to create another dowel joint and use wood glue to securely hold the seat in place. A nail gun is also great for nailing the seat to the back legs from behind.
The next step is to brace the legs. Run a 1×4 inch board around the outside or inside of the legs on the underside of the chair seat. Measure, cut, and attach each board connecting all legs together. It's also a good idea to place a diagonal brace piece from each support board to another, creating an octagon appearance. Metal braces are also sturdy, inexpensive options. Glue everything into place after attaching each piece with screws or a nail gun. Allow the wood glue to set before going any further.
Now you're ready to attach a brace across the top of the chair, connecting the two back legs. Work with this piece of wood for a while and test your hand at some planning skills. Plane out about one-half inch of the wood to create a comfortable place for your back to rest. You may want to do the same to several boards for a ladder back chair. If you want to use spindles for the back, simply order a quality wood dowel that matches the rest of your wood. Drill holes in the top board and chair seat, use wood glue, and assemble the chair back.
After everything is dry, your chair should be ready for years of quality use.