If you're asking what one might find inside a castle, the answer is: it depends. Castles were built for many different purposes, from royal residences to fortresses, and so their contents varied greatly. However, there are some features that were common to most castles.
One of the most important features of a castle was its defences. Castles were built to withstand attack, and so they were typically equipped with thick walls, strong gates, and sometimes even moats.
Inside the walls, castles would typically have a great hall, where feasts and other events were held, as well as a chapel for religious services. Other common features included a kitchen, stables, and living quarters for the castle's occupants.
Of course, the contents of a castle varied depending on its purpose. For example, royal residences would often be filled with luxurious furniture and tapestries, while fortresses would be more sparsely furnished. But regardless of its purpose, a castle was a symbol of power and wealth, and so its contents were always impressive.