John alternates back to sharing the signs of Jesus as the Messiah in this chapter, where John 5 was primarily focused on a discourse. This time, we see signs 4 and 5.
These are actually two of the most famous miracles of Jesus. The first one is present in all four Gospels. Outside of the last week of Jesus, the Passion Week, it's a rarity to find something in all 4 Gospels. The birth of Jesus isn't in all four. Several events in John (Nicodemus, Cana, the woman at the well) are only in John...and so forth.
There are some useful details here, such as the extended interaction with the disciples about the food situation. It's also from John 6:15 that we see Jesus aware that the crowd wants to make Him king by force...and so He withdraws.
Then He walks on water, making the fifth sign. Peter's dip into the waters is not mentioned at all, and then the boat gets where it was going.
What do we do with either of these?
Put them in context with the teaching passages. Jesus finishes out the section pointing out that the Israelites had eaten manna, bread from God, in the wilderness back in Exodus. Now, He has fed them with bread. I think left unstated is that Jesus has shown that parting the Red Sea isn't necessary again, because Jesus can walk on the water and Peter (showing those who follow in faith) could, too.
Except the people got hung up on the first part. They did not grasp the idea of Jesus Himself being "the bread" rather than just providing them food. It was a metaphor that they could not wrap their heads around, and so they just shut down on Him.
Do we ever do that? We hear something being taught and then stop listening? Maybe it was too hard to understand, or just too different? Or worse, it was easy to understand and hard to do, so we didn't do it.
Then we wonder why we don't have the rest of the information, the rest of what we wanted to know. And it's because of this: we never got the first part.
It's like baking a cake and skipping the "preheat the oven" stage. Get the first thing right...and remember that when it's time to add eggs, it means out of the shell, too. You have to do what God has said to understand what He said to do next.
More on John 6 is here