Luckily it only takes a second to check your coolant level. Most cars these days have a translucent coolant overflow tank right next to the radiator. It's white plastic, but you can see inside to see if there's enough juice to keep things safe. You'll also see markings on the side telling you the low and high levels to work with. Always check your coolant level when the car is cold.
If you happen to have an older vehicle without a visible overflow and fill tank, you'll have to check the antifreeze / coolant level by looking into the radiator. There is no dipstick or other meter to tell you whether you have enough coolant in the radiator on these older vehicles. The good news is that the older systems were much less sensitive to how much coolant you had -- or didn't have -- in the radiator. As long as you can visibly see the level of the coolant by removing the radiator cap and looking into the top of the radiator, your level is fine. The following piece of information is very important: Do NOT attempt to open the radiator cap on a hot car.
The system is highly pressurized and the fluid inside is very hot. The combination of the two can mean some serious burns if it starts to spray out. Patience.
If your levels are good, no need to go any further, enjoy the peace of mind. But if you're low, you'll need to top it off. Your engine takes a 50/50 mixture of coolant and water. That's a mixture of half water, half coolant In the old days, you had to make measurements yourself and test the mixture to get it right. But since we live in the age of convenience, you can now buy premixed coolant that's ready to pour. For a simple topping off, I recommend going this route. It might cost a buck more, but you're in for much less mess.
To add the coolant, simply unscrew or pop off the cap on top of the opaque plastic overflow reservoir and add your mixture until it reaches the full mark. Now put the cap back on nice and tight and you're ready for any weather.