What is the difference between a basilica a cathedral an oratory and a church?

A cathedral is the chief church of a diocese in which the bishop has his throne.

Basilica has both an architectural sense and a canonical sense. In the canonical sense, the term usually refers to major buildings. Major basilicas include St. Peter's, St. John Lateran, St. Mary Major, and St. Paul-without-the-Walls... one of the features of major basilicas is that they have a "holy door". The pope can declare a particular church as a basilica.

"Chapel" is a very broad term, and can apply to anything from a section of a much larger church or cathedral, to small buildings. The word itself is associated with the idea of relics, since it is drawn from the idea that St. Martin divided his cape (chapelle) in half and left half with a beggar.

"Church" is a word that covers pretty much everything given above... generally any building set aside "in perpetuity for the public exercise of Divine worship."

As a general term, Oratory signifies a place of prayer, but technically it means a structure other than a parish church, set aside by ecclesiasticalauthority for prayer and the celebration of Mass. Oratories seem to have originated from the chapels erected over the tombs of the early martyrswhere the faithful resorted to pray, and also from the necessity of having a place of worship for the people in country districts when churchesproper were restricted to cathedral cities. We also find early mention of private oratories for the celebration of Mass by bishops, and later oforatories attached to convents and to the residences of nobles. In the Eastern Church, where the parochial organization is neither so complete nor so rigid as in the West, private oratories were so numerous as to constitute an abuse.