You have 200amps service (provided the feed to your house is actually the correct rated wire and some fool didn’t install the incorrect breaker on in underrated wire)

The only way to know for sure how much you are using would be to watch your meter and do the calculations to convert watt hours to amp hours…or put an ammeter on your mains.

The other way would be to inventory everything you plug in and look up in the spec sheets to add up all the power requirements to estimate your home’s load.

The final way you could look at it would be, “hey, this panel has a few empty slots for breakers. Let’s tap into it.”

Now, just because you have empty space you might want to ask, “is this panel a known fire hazard?” Yes, some panels are notorious for flaming up and are recommended to be changed.

The next question is whether you can even find breakers to install into that panel. Sometimes what the local hardware store stocks is not the type of panel you have installed in your home.

After you start to learn about all of this, ask yourself, “is this something I can confidently do myself?” May it will be or you should just call an electrician and ask for an evaluation and estimate to install the plug.