The first thing I always tell people when they first start a Bethesda game is that exploration is going to be your best friend. Fallout 4 (and Bethesda's other games) are meant to be explored and some of the best moments are when you stumble on something new or random when you go off the beaten path.
Fallout 4 is full of tons of random events, characters, and secrets and some of them are going to be hard to find. It's also full of things to loot including bottlecaps (the game's currency) and powerful Legendary Weapons and armor pieces that could help you turn the tide in difficult parts of the game.
You can avoid the main quest for as long as you want though I suggest playing it at least until you hit the first big city.