Outlook has two Finds: the simple Find which displays a Find pane above your message or item lists and Advanced Find which opens the Advanced Find window. Many times, you can find what you need using the simple Find and it searches multiple folders and items types.

Tips to improve your searches:

1. Use commas to separate multiple keywords. (This OR's the keywords together.)
2. Use the Options menu at the far right to search all text. With this option unselected, only a limited number of fields are searched--the fields depend on the item type, but are generally restricted to the Subject and From field.
3. Select the folders to search in using the Search In menu following the Look for box.