It's early one morning after Peter and the other disciples had been working (fishing) all night. They'd worked all night, but caught nothing.
Yes, worked: keep in mind this isn't recreational, out-with-a-buddy-and-a-six-pack type of fishing.
Fishing was Peter's (and James' and John's) occupation. It was their job, the way they made a living.
So they've worked all night, but caught nothing. It's been a fruitless, unproductive time.
Then, at daybreak, as they're pulling into shore, something strange and unexpected happens.
A "stranger-whom-they-later-realize- is-Jesus" (I'll say more about that dynamic in Sunday's sermon) tells them to try something new (I'll say more about that in Sunday's sermon, too) and so they cast their nets on the other side of their boats.
This results in a miraculous catch …