Don't mix up 'lie' and 'lay'. You lay something,
as in they are going to lay the carpet, but you lie down on
a bed or other flat surface. Sentences such as he is laying on the bed
or why don't you lie it on the bed? are wrong: correct forms are he
is lying on the bed and why don't you lay it on the bed?
The past tense and past participle of 'lay' is 'laid', as in they
laid the groundwork or she had laid careful plans; the past tense
of 'lie' is 'lay' (he lay on the floor) and the past participle
is 'lain' (she had lain on the bed for hours).
