Something with availability is easy to get or to access. If you work at an ice cream shop, the availability of ice cream might make it hard to stick to a diet.
The noun availability indicates that something is easily obtainable and ready for use. If you are thinking about renting a certain apartment, you might want to ask about the availability of parking spaces in the neighborhood before you sign a lease. You can use availability and accessibility almost interchangeably, as with this sentence: "The accessibility of the Internet has increased the availability of information."