When something is available, you can get it or you can have access to it:
Books are available for you to use at a library.
A good education is available at public schools.
John needs to get to the airport. Is there a cab available?
There aren’t any offices available for rent in the building. They’ve all been rented.
The bathrooms on this floor are unavailable because they’re being renovated.
I need to see the doctor. Are there any appointments available for this afternoon?
A person can also be available:
The doctor is available after 2 p.m. this afternoon.
Our teacher is available to speak with students after class is over.
U.S. military forces are available around the clock.
Emergency services are available 24/7.
Mr. Johnson isn’t available right now. You’ll have to leave a message on his voicemail.
When are you available today?
The word "availability" is a noun:
The availability of some natural resources is limited.
Let me check my availability for that day.
Whether or not she can make the meeting depends on her availability.
Is she available today?
Note: Sometimes the word "available" is used to describe a person who is not currently in a romantic relationship. If a man or a woman is available, he or she does not have a wife or a husband, a girlfriend or a boyfriend.
A: Tony thinks Denise is hot.
B: Really? She’s available. He should give her a call.
Is she available today?