It should be a rectangular plastic tank with a cap on top.
Here are some tips to help you find it:
* Look for hoses: Follow the windshield washer hoses from the windshield washer nozzles towards the engine compartment. The reservoir will be at the end of these hoses.
* Check for labels: The reservoir might have a label that identifies it as the washer fluid tank.
Once you've located the reservoir, simply unscrew the cap and pour in the washer fluid. Make sure to use a washer fluid that's designed for cold weather conditions, especially if you live in a climate that experiences freezing temperatures.
Let me know if you have any other questions!