The first line defines which devices the code will apply to. In this case, it will only apply to devices that are 768px or up wide. The second line sets the same style for all devices that are wider than 768px.
/* Medium devices (tablets/desktops, 768px and up) */
@media screen and (min-width: 768px) {
}
/* Large devices (large laptops and desktops, 1168px and up) */
@media only screen and (min-width: 1168px) {
}