“I had a headache, so I lay down on the couch.”
“Every morning the chicken lays an egg.”

It is very easy to confuse “lay” and “lie” in English. In the present tense, “lay” means to set something down (it takes an object). “Lie” means to rest on a surface (it doesn’t take an object). It is more confusing because the past tense of “lie” is also “lay” (the past tense of “lay” is “laid”). So yesterday, the hen laid an egg, and now, I will lie on the couch.