The first thing that you need to do is to get yourself two pieces of wood. If you are making a wooden cross for the purpose of using it as a primitive funeral cross, then you do not have to worry about the pieces of woods being flat and consistent. Both rounded or flat wood would do. On the other hand, if you planning on making a crucifix, then you will need your pieces of wood to be flat and consistent.
Use a handsaw to make one of the two pieces shorter than the other. Try to cut the wood as cleanly as possible. You will now have one piece of wood of original size and another piece of wood that is relatively shorter.
For a primitive funeral cross, bind the two pieces of wood together using a rope or string in such a way that they form three short legs and one comparatively longer base.
If you are making a crucifix, form notches in both the pieces of wood first so that they fit nicely together and then bond them in that position using a nail and hammer. Again, make sure that the pieces of wood are joined in such a way that there are three short legs and one longer base.
Many crucifixes have a small Christ figure hanging right where the three legs and base meet, signifying the crucifixion of Christ. Get your hands on a small figure and stick at the aforementioned point on the cross using strong glue.