Inventory forecasting

Hello

Im a new poster, a non techy and a fairly basic level Excel user who is trying to learn more! I'm needing to produce a stock forecast and I want to learn how to use the Excel "Forecast" function. I'm using historical monthly demand figures, but I also want to be able to create an uplifted forecast for particular months to allow a seasonal winter adjustment. Is anyone able to help me by explaining more simply the best way of using this function (Im finding the Excel help terminology quite complicated at my level). Or does anyone have a simple example they would be willing to share with me to show me how?
Many thanks for any help - I would be very grateful!

Cheers

Wow - thanks so much for these - really appreciate the pointer - I will work through and have a go.