How to use まるで

まるで "marude" has two basic meanings:

1. "just like"

When used in this manner, まるで is often followed by よう or みたい.

スミスさんは日本語が上手で、まるで日本人（のよう）だ。
Sumisu san wa Nihongo ga jouzu de, marude Nihonjin no you da.
Smith is good in Japanese that he speaks like a Japanese.

あの老人はまるで赤ん坊（みたい）だ。
Ano roujin wa marude akanbou mitai da.
That old man is just like a baby.

2. "completely"

In negative sentences, まるで has the same function as まったく "mattaku" and ぜんぜん "zenzen". However, まるで implies the speaker's negative judgement.

Reference:
Miura, Akira. Essential Japanese Vocabulary, Tuttle.