These are two different verbs: one means: to be positioned horizontally (lie) and the other to position something else horizontally, to put something down (lay)
They sound similar and have a meaning connected to being horizontal, that's one reason for their confusion.
Make sure you also don't confuse their past tenses:
Lay: laid
lie: lay
Yes, Lay is the present tense of one of them and the past of the other: that's the other reason for their confusion!
