Example: I am looking for information about the effects of carbon dioxide on vegetation and climate change.
Separate out three concepts: carbon dioxide, climate change, and vegetation.
(This gets climate or climatology as well as climatic)
Example: vegetation or plants
This would find articles with the word "vegetation" or "plants".
AND Generally narrows your search and focuses it.
Sometimes and can broaden your search. Instead of typing "climate change", type the two words together with the and connector. This will find the two words in any order, as in the sentence: "changes in climate due to vegetation..."
Example: climate and change
And also narrows your search by making two or more terms be together in a single record.
Your final search would look something like this. You MUST use parentheses around the words you "OR" together.