Lay down has several different meanings.
If you lay something down it can mean you officially establish a rule, or officially state the way in which something should be done.
Please follow the rules laid down by the administrator.
If you lay down your weapons it means you stop fighting.
They laid down their guns and surrendered.
If you lay wine down it means you are storing it in order to drink it in the future.
I laid down this bottle in 1998, it should be perfect for drinking
For example: "If you are tired lie down and have a rest."