Here are a few resources you can use if learning about the Composer Antonio Vivaldi:
Great pieces to listen to:
YouTube – Guitar Concerto in D major
YouTube – Violin Concerto in A minor Op. 3 No. 6
Classics for Kids – has short radio shows on Vivaldi’s life and compositions, including one on violin concertos.
Baroquemusic.org – An interesting site with biographical information as well as many other links to relevant information