Present: I lie on the grass / I am lying on the grass Past: I lay on the grass / I was lying on the grass Be careful. 'to lie' and 'to lay' are two different verbs. To lie = to be in or put yourself in a horizontal position. e.g. I LIE down to rest. The 'ing' form is LYING. The simple past is LAY. The past participle is LAIN. To lay = to put down or put in position horizontally. e.g. I will LAY the rug on the floor. The 'ing' form is LAYING. The simple past is LAID. The past participle is LAID.

In present , we say " I lay on the grass to rest". In past tense "I laid on the grass to rest". In preset continuous tense " I am lying ont he grass to rest". Hope this helps. lying is continuous..you are still doing that action.