Minecraft is designed with two basic modes or play-styles.
Creative mode operates as a virtual sandbox, opening up access to all resources for experimentation, building and creativity. You can play mob-free and even flying is permitted.
Survival mode is difficult without any prior knowledge. There is an underlying plot, but it is not driven by the plot. There is way more to the game than surviving on a hilltop, and I am not convinced that anyone would be able to discover the underlying plot without helpful hints and crafting recipes found online.
When starting a survival game, know that there are day and night phases, you start at the beginning of the day, and must begin preparing for night, as mobs (monsters) can generate anywhere nearby you where there is darkness and will attack you immediately. Survive by gathering things like dirt or wood that when placed on the ground, will help isolate you from them, spend the next day upgrading your shelter, tools and gear (crafting recipes will help, but if you have the time and the will you can experiment by opening the inventory menu and dragging items you've gathered into the four crafting blocks next to the avatar of your character.
A couple of recommendations: when it comes to crafting tools and complex items, you will have to first find out how to make and use a crafting table. Once you have a shelter location picked out, locate and kill some sheep for wool and combine it on the crafting table with wood for a bed - once you sleep at night, you will skip the night altogether, mobs will not spawn or attack, and if you die you will re-spawn next to it.