An execution or punishment involves beinghead; someone's head might be cut off during this.
To behead someone usually means to remove their head from their body. This can happen as a form of punishment or in a war setting. Imagine reading about an ancient king who ordered his enemies to beheaded - that's what this word does: it describes the act of cutting off heads, often as a form of revenge or execution. Sometimes, a leader might order someone beheaded because they betrayed them, and other times it can happen during battle when one army is capturing another. In both cases, beinghead means losing your life in a very final way.
To remove the head of; to cut someone's head off.
