When you extrapolate, you use specific details to make a general conclusion. For example, if you travel to Canada and encounter only friendly, kind natives, you might extrapolate that all Canadians are friendly.
The verb extrapolate can mean "to predict future outcomes based on known facts." For example, looking at your current grade report for math and how you are doing in class now, you could extrapolate that you'll likely earn a solid B for the year. Another meaning of extrapolate is "estimate the value of." You could extrapolate how much your antique watch is worth by finding how much similar watches sold for at recent auctions.