どちらも「牛乳残っているよ。」という言い方です。
1)There's still some milk in your glass.
2)There's some milk left in your glass.
You didn't finish your milk. とも言えます。
例えば「お皿に人参残ってるよ。」と言うなら、
There are still some carrots on your plate.
There are some carrots left on your plate.
または
You didn't eat all your carrots.
などとも言えます。
ご参考になれば幸いです!