We use look to talk about concentrating, paying attention, trying to see what is there. You can see something without wanting to, but you can only look at something deliberately.

For example:
I looked at the photo but I didn't see anyone I knew.

When look has an object it is followed by a preposition.
Look at me! or I was looking for a new CD.

There are many two part verbs and idioms that use look.

1. To Look Up: to locate information in a directory, dictionary, book, etc.
I often look up information on the internet before I travel.

2. To Look Out For: to be careful or cautious.
Be sure to look out for deer on the highway when you are driving at night.

3. To Look Over: to examine, to inspect closely.
Always look over your notes before a test.

4. To Look Into: to investigate, to examine carefully.
I am looking into taking some new courses at University.

5. To Look Up To: to admire, to respect greatly.
The person I look up to the most is my mother.

6. To Look Out On: to face, to overlook.
The cabin looks out on a beautiful green lake.