Purpose using に

This is a basic way of saying,
"I'm going somewhere to do something."

LOCATION に PURPOSE に MOTION VERB.

The first に marks the location that you are going/coming from.
The second に marks your purpose.

I the "purpose" part of the sentence, you must use STEM FORM or an activity noun of a verb.

EX: 
Location    に         PURPOSE        に    MOTION VERB
    うち       に    ばんごはんをたべ    に    かえります。
                     I go home to eat dinner

がっこう     に   しゅくだいをだし     に    いきます。
        I go to school to turn in my homework.

とうきょう  に    ともだちにあい       に    きます。
           I come to Tokyo to meet my friend.

スーパー     に         かいもの           に   いきます。
            I go to the supermarket to shop.