When using 对 (duì) as a preposition, it is used to indicate "to" or "towards" a object or target. As with all prepositions, some care should be taken when using this particle, as usage of 对 doesn't always totally "make sense" or correspond to English at all. 

Basic Structure
The structure is basically:
对 + Object + Verb Phrase
Note that you shouldn't be plugging in just any old verb here. Certain verbs are often used with 对, and some even need 对 if you want to add an object (like 感兴趣, explained below).

Examples

Tā duì wǒ xiào.
他 对 我 笑。
He laughs at me.

Wǒ yào duì nǐ fùzé.
我 要 对 你 负责。
I am going to be responsible for you.

Tā duì wǒ hěn kèqi.
她 对 我 很 客气。
She was very polite to me.


Nǐ wèishénme duì wǒ yǒu yìjiàn?
你 为什么 对 我 有 意见 ？
Why do you dislike me?

对 is also used in such structures as: 对……来说 ("for... [a person]") ,对...感兴趣 ("to be interested in...") as well as 对···的印象（”the impression on the object“）
对……来说

This essentially means "for... (a person)." It's for making a statement from a certain person's point of view.
The pattern is:
对 + Person + 来说

Chuāncài duì wǒ láishuō tài là le.
川菜 对 我 来说 太 辣 了。
To me, Szechuan food is too spicy.


Duì tā láishuō yīnɡyǔ hěn rónɡyì.
对 她 来说 英语 很 容易。
She thinks English is easy.

Duì wǒ láishuō shūfǎ hěn yǒuyìsi.
对 我 来说 书法 很 有意思。
I think calligraphy is very interesting
.