Your first order of business after getting into the game is to start collecting some raw materials since you start with no items in your inventory. There is no set starting point In Minecraft. You are just put into a randomly generated world with completely random surroundings. No matter what biome that you start in, the first thing that you want to find are some trees. Trees will supply you with the materials you'll use to make your first tools and shelter.
Most of the actions in the game occur from left clicking with an item selected while it is on your hotbar. Since you will not have any items yet when you harvesting the wood, you simple have to walk up to the tree and hold down the left mouse button until the wood breaks apart and falls onto the ground. You then walk over it and it will appear on your hotbar. Once you have about five wood blocks, you need to create wood planks from the raw wood. To do this, you open your inventory and click on the blocks and move it to the 2x2 crafting window in your inventory. For every one wooden block in the crafting window, you get 4 wooden planks. Next you're going to take four wooden planks and put them into the 2x2 crafting window. You'll put one in each slot. This will create a crafting table. Put the crafting table on your hotbar, and place it by exiting out of your inventory and right clicking on the ground where you want it placed. The crafting table is where you will make most of your tools. These tools include a pickaxe, shovel, axe, and a sword. You will make this first round of equipment from wood.
A large part of playing Minecraft is knowing the recipes to create new items. You can find all of the item recipes online at the Minecraft Wiki. It is highly recommended that you check out the Wiki because it provides a lot of helpful information. There isn't very much interaction with Minecraft outside of being in-game. When playing single player, the world automatically saves the environment and your character when you exit the game. There's also a multiplayer mode where you can play with other players in a variety of scenarios depending on the server. You can change the way your character looks on other servers by changing its skin. The best way to find out how to do this is by Googling for a tutorial.