When the top of the soil gets dry, you should water it.
Put the plant by the window, but not outside directly under the sun.
ーWhen the top of the soil gets dry, you should water it.
「土の表面が乾いたら水をあげてね」
top of the soil で「土の表面」
water は動詞だと「水をやる」という意味になります。
ーPut the plant by the window, but not outside directly under the sun.
「植物を窓際に置いてください。でも外の直射日光の下には置かないでください」
by the window で「窓のそばに・窓辺に」
directly under the sun で「直射日光の下に」
ご参考まで!