Recitative is characterized by its parlando style, which means that it is sung in a manner that is similar to speaking. The melody of a recitative is usually simple and follows the rhythm of the text. Recitative is often accompanied by a continuo, which is a group of instruments that provides harmonic support.
Aria is a more formal and structured musical form than recitative. Arias are typically composed in a da capo form, which consists of an A section, a B section, and a return to the A section. The A section of an aria is usually the main theme of the piece, while the B section provides contrast. Arias are often accompanied by an orchestra, and they can be very elaborate and virtuosic.
The main difference between recitative and aria is their function. Recitative is used to advance the plot of an opera, while an aria is used to express a character's emotions. Arias are often used to showcase the singer's vocal abilities, and they can be very beautiful and moving pieces of music.