Methane CH4 is sp3 hybrid and as such has a tetrahedral geometry. Recall from gen chem the concept of VSEPR (valence shell electron pair repulsion). With VSEPR the things or ligands or atoms or electrons (lone pairs) projecting from a central atom will repel one another. They push away from one another as far as possible. For sp3 systems like methane it has 4 hydrogens embedded in orbitals (electrons), so these four hydrogen push away from one another so they are as far away from each other as possible. It's as if they are pushed into the 4 corners of a cube or box.