How can I give a speech to the audience at school so they know and understand how the Gospels apply to real life?

A good strategy for relating the Gospels to real life might be to take a cue from Jesus. To illustrate the lessons he preached throughout the Holy Land, Jesus used parables. Parables are tales that briefly explain important moral lessons for people to live by, particularly people who identify as Christians. 

For example, Jesus' parable about The Good Samaritan, which appears in the Gospel of Luke (10:25-37), is applicable to many situations in our lives. The story talks about a traveler who lays sick and dying on the side of the road. Two supposedly virtuous people pass him by before a Samaritan takes notice and helps him. The Judeo-Christian teachings of The Good Samaritan are usually connected to lessons of looking after one's neighbors, treating others as you want to be treated, and virtuous actions are more important than pious words. 

Relating this parable to contemporary situations should be fairly easy. A discussion of inviting a new person to the lunch table, like someone who is lonely or bullied, is one example. Encouraging acceptance of others in one's community, like those of different cultures or religions, would also be an appropriate parallel. Finally, recommending spending time volunteering at a soup kitchen or nursing home rather than spending time sharing memes — even socially conscious ones — online would connect to the axiom actions speak louder than words.