Hi Robert,
This person must be a real good friend, not to many people give away an ATV...
I am not an expert with regards to Polaris, but I will give this a shot. Alot of older ATVs don't actually have a "dipstick", I know my 89 kawasaki doesn't.
Instead, there is a "window" on one side of the motor. It is a small glass window, and varies in size from the size of a nickel, up to the size of a quarter. Usually the oil level needs to be about halfway up the window. If it is not showing, or showing at the bottom of the window, you need to add some oil.
On top of the "case", you will probably see a small cap, you remove that to pour in the oil. If it is really dirty, clean the area before you remove the cap, this will keep any dirt or crud from falling in and contaminating the oil supply.
If you will be keeping the Polaris for a while, you might want to think about a repair manual, to answer questions like these, as they come up.
Here is a link to order that manual, just in case your interested...
http://www.atv-411.com/polaris-atv-repair-manual-2.html
This manual costs about 20 bucks, plus shipping. When the page loads, click on the picture of the manual, and it will take you to the order page.
Hope this helps, let me know if you need some more info.
Ride Safe. Ride Legal. Ride Again...Curtis