Let me explain. First, there is no confusion when you mean to say something that is not true,” such as “he told a lie.” So forget about that.
When chickens lay their eggs, they place something somewhere. “They will lay their eggs in the boxes.” So when we place something in a position, usually horizontally, we lay it. For example, “we lay the table.” “The soldiers laid down their arms.” “We will lay the body in the coffin.” “Please lay a drop cloth on the floor before you paint.” “Lay” is what’s called a transitive verb where the subject of the sentence does something (the action of the verb) to an object. For example, “I’m going to lay the baby on the blanket”
Lie is what’s called an intransitive verb. It doesn’t take a direct object. “I’m going to lie down.” “The island lies in the middle of the lake.” “The baby lies quietly sleeping.” “Papa is lying in the hammock.” Confusion can come with the past tense: “The weapon lay on the floor”.
The confusion probably arises because these verbs share “lay.” “Lay” is the present tense of the transitive verb “lay” and is also the past tense of the intransitive verb “lie.” When in doubt ask yourself, “Lay what?” or “Lie where?”