When he lieth down, that thou shalt mark the place where he shall lie, and thou shalt go in, and uncover his feet, and lay thee down; and he will tell thee what thou shalt do. 3:4
Naomi (Ruth's mother-in-law) advises Ruth as to how to best seduce Boaz.
She tells her to wait until he is a bit drunk and has fallen asleep. Then "go in and uncover his feet
[a biblical euphemism for male genitals], and lay thee down; and he will tell thee what to do."
3:3-4
Ruth does as Naomi says, and then at midnight Boaz wakes up and finds Ruth "at his feet." He asks who she is,
and she says, "I am Ruth thine handmaid: spread therefore your skirt over thine handmaid."
3:7-9
Boaz seems agreeable to the suggestion and says, "I will do thee all that thou requirest." Next he asks her to
"Tarry this night ... lie down until the morning." so Ruth "lay at his feet until morning."
3:11-14