As so often avocado are delicate to transport when really ripe, hence most of the time avocado on the market are prematurely harvested and hard - inedible. To properly select an avocado fruit - squeeze gently between thumb and index finger - a ripe avocado may have a hardness of butter when NON-frozen but cold when stored in the fridge.
To eat - may ways are used. Traditionally in the Philippines avocado is eaten by many with sugar, while in western world we often use avocado in salad or we prepare the world famous Mexican Guacamole recipe.