Searching an array for key word lists with php?

The Scenario

Basically I have a search function that will search a database for what ever the user is typing. My plan was to first search for the full string they entered then explode the sentence and search for each key word for example.

User enters: How to volunteer with some company.

I would search for that full sentence then explode it but I don't want to search the database for words like

"us, i, it, the" etc or even the company name which would return every single page. So basically in this example trimming it down to only "volunteer" and searching for that.

I would like to know how to detect and remove all low level words such as (the, and etc) leaving behind words like (volunteer, member, reception etc). I don't wish for people to spend ages coding a function just to inform me what function I should be using would be more than sufficient.

Any help would be appreciated or if you think I should be doing this another way I would appreciate the input. Thanks