The prefix syn- means "same." "Optic" refers to seeing; therefore, the "synoptic" gospels see the same things. Many of the events related in Matthew, Mark, and Luke are the same, while the Gospel of John takes a different perspective. Although Matthew, Mark, and Luke have different authors who each take a different approach to Jesus' life, many of the parables, miracles, and sermons recorded can be found in two or three of these gospels. For example, the parables of the sower, the mustard seed, the tenant farmers, the budding fig tree, and the new cloth on the old garment appear in all three synoptic gospels. Nevertheless, each gospel relates at least one parable that is unique to that writer's account.
Regarding miracles, all three synoptic gospels and John tell of Jesus' feeding the 5000, but only Matthew and Mark tell of feeding the 4000. All three synoptics relate healing the paralytic, calming the storm at sea, and casting the demons out of the demoniac of Gerasene. It is rare for any of the synoptic gospels to tell about a miracle that no other gospel relates; conversely, the Gospel of John is the only gospel that describes turning water into wine, healing the man born blind in Jerusalem, and raising Lazarus from the dead.
To get a continuous, chronological presentation of the material provided in all four gospels, you can use a "harmony of the gospels," either online or in print. This is a good way to see which material is repeated between the gospels and which is unique to one of them.