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Consider for a moment what is known as the isolobal concept, there are a series of atoms and groups which all present the same types of orbitals (or at least close to identical orbitals) and the number of electrons.
Consider for a moment a methane molecule, if we were to break a C-H bond then the carbon atom would only have seven valance electrons. The carbon in an alkane such as methane has rehybridized its orbitals to give us four sp^3 orbitals. These are arranged in a tetrahedron around the carbon.
A covalent bond is formed by sharing the one electron in the sp3 orbital of the carbon with an atomic orbital from another atom that has the right geometry to overlap with the sp3 orbital. The sp3 orbital has two pear-shaped lobes, one is large and one is small. These have opposite signs of the wavefunction.
A hydrogen atom in the ground state has a single electron in an s orbital, this is a sphere-shaped orbital that can interact with the sp3 orbital to form both a bonding and an antibonding orbital. We will only concentrate in this answer on the bonding orbitals.
The sphere-shaped s orbital has the right geometry to interact with the sp3 orbital and it can result in the formation of an occupied (2 electrons in it) bonding orbital between the carbon and the hydrogen. This will be a sigma bond (single bond)
If we change to chlorine, then the outermost orbital (for the valence electrons) of the atom has also rehybridized to give us four sp3 orbitals. Three of these are occupied with two electrons while one in an isolated chlorine atom only has one. The orbital with only one electron can interact with the sp3 orbital on the carbon (bearing only one electron) to form two new molecular orbitals. One is antibonding and one is bonding.
If the bonding orbital between the carbon and the chlorine is occupied with two electrons then we have a bond. The C-Cl and C-H bonds will be different in length. But the angle between them will be dictated by the arrangement of the sp3 orbitals around the carbon atom.
If you still do not understand it then I would suggest that you fall back to VSEPR theory. As it is the festive season go and grab an orange and four cocktail sticks. Stab them into the orange in such a way that they are the greatest angle apart. You should find that the tips of them form a triangle-based pyramid (tetrahedron). It will not matter if you put grapes on the points of the cocktail sticks to represent hydrogen atoms in the methane. Or apples to represent the chlorine atoms in carbon tetrachloride. You will still have the same arrangement of the atoms in your model.
You can then hang it on the tree as a decoration or pull it apart and eat the fruits. When I can not lay my hands on my molecule modeling kit made of plastic balls and straws I tend to grab oranges and then draw atoms with a marker pen on the skin.