While the details vary depending on the type of loom you wish to build, the simplest frame looms require only building a rectangular frame out of wood and then wrapping yarn for a warp. Other types of looms, such as inkle looms or looms with heddles, require more steps.
Any type of loom needs a frame to hold the warp, the foundation of yarn that does not move, in place. A frame loom is called that because the wooden frame composes the entirety of the loom. These looms are simple and can be used for basic projects like napkins and pot holders. The size of the frame generally limits the size of the final project.
Inkle looms have a frame that contains a series of pegs. These pegs allow for a much longer warp to be used, and inkle looms offer an ideal way to weave belts and straps.
Table and floor looms are generally more complicated. The frame often has a rotating bar on each end, which again allows for a much longer warp. In addition, they often have one or more heddles, a kind of guide that holds the warp threads, separating them in various patterns. This allows the weft, the yarn that's being woven back and forth, to create intricate designs while the weaver maintains a high speed.