Before you go
There’s a big sign at the entrance to a parking lot.
What it says is usually one of these two.
空車
満車
Even if you can barely read any Japanese, these two are worth remembering.
空車 = there’s space
空車
It means there’s a space you can park in.
In English it’s close to Available / Vacancy.

If the entrance says 空車, there’s space available.
満車 = it’s full
満車
It means there’s no space left to park in.
In English, Full.

If it says 満車, look for another parking lot.
Inside a building, just the one character 空
In a multi-story or underground garage, you look for a space once you’re in.
The signs there sometimes use just the one character 空.
It means the same as 空車.
It says 満車, but you can see an empty space
That happens.
The space you can see may be marked
月極 — for people with a monthly contract
カーシェア専用 — car-share only
or something similar, and ordinary cars can’t use those.
When the entrance says 満車, driving on to the next lot is quicker.
Go by the characters, not the color
Electronic signs use color differently from one parking lot to the next.
What’s worth learning is the characters: 空車 and 満車.
※ How 空車 and 満車 are displayed, and how you drive in, differ from one parking lot to another. If there’s a signal, a gate or an attendant at the entrance, follow their guidance.