Anything operable can be used, or it can be operated on. Now that you've replaced the flat tire on your bike, it's operable. And that boil on the tip of your nose? That's also operable (Whew!).
Things that work or are ready to be of service are operable, like the vacuum cleaner that's been tuned up and has a brand new bag in it, your new waffle iron that you've seasoned and plugged in, or the mayor's extensive plan for reducing homelessness. Another, much more medical way to use this adjective is to mean "able to be treated with an operation," like an operable knee problem or operable skin cancer.