Gospel is a word that means Good News. It involves the wonderful message about Jesus' birth, life, death and resurrection and how that provides for the salvation of everyone who accepts it as a free gift by faith.
The four Gospels in the New Testament are four particular books written by different authors, some eyewitnesses of Jesus to explain his life, impact and death. They vary in aim, length and selection of material and provide complementary views. They are books of Good News.
Mark's Gospel is a good one to start with if you are reading the Bible for the first time. It is good to suggest to new believers to read this book over and over again. Mark is quite short so this is practical and the repeated re-reading helps to cement the general overview of the life of Jesus.