You begin the game inside of your tree house. Exit the house. When you exit, your friend Saria will run over and speak to you. After she stops talking, climb down the ladder.
You will notice that there is a map in the lower right hand corner of the screen. The yellow mark represents you and it points in the direction in which you are facing. The red mark represents where you last exited a building or dungeon and appeared on the map (in this case, the red mark signifies the tree house). You can divide the map into two basic sections with your eye - the left section, which we will call the Forest, and the right section, which we will call the Deku Tree. These two sections, as you can see, are connected. We will first concern ourselves with the Forest section of the map (the left section). You will notice that your tree house is located in the southern part of the Forest. On the map, you can see a path that leads off from the west of the Forest. That is the exit from the Forest, which you can not yet leave, for it is blocked. To the north is the entrance to the Lost Woods. To the east is the path leading to the Deku Tree, which is also blocked. To obtain access to the Deku Tree, you must first find the Kokiri Sword and buy the Deku Shield.
First, we shall find the sword. Start walking from the tree house to the western exit from the Forest (use the map as a guide). When you are about 3 quarters of the way to the exit, you will see an incline on the left. Proceed up the incline and follow the many signs through a fenced off section of the Forest. Eventually, you will see a small opening. Walk up to the opening until you see the word "Enter" on the action icon (that is the blue button displayed at the top of the screen which corresponds to the "A" button on your control pad - I will be referring to this button as the "action icon" from now on). Then press "A" to perform the indicated action, which was "Enter." You will begin to crawl, which is something that you can only do as a kid.
(Note: There are two growth stages in your quest, you are relatively young in one stage and relatively old in the other - I will be referring to the present young stage as "kid" and the future older state as "adult" from now on.)
Press upwards on the joystick to crawl further until you can stand up again. Walk and face left at the intersection. Stand still for a bit and you should start to see a huge boulder rolling around. Follow the boulder and move into the little side openings (while avoiding the boulder at all costs) until you come to an opening with a treasure box. Walk up to the treasure box and press "A" to open it. It will be the Kokiri Sword. Press Start and move to the screen that shows a picture of your character and then select the sword with the "A" button. This is called "equipping," which is also a term that I will be using and I will from now on assume that you know how to do it. You can take out the sword and swing it with the "B" button. It's not that complicated - you'll become very good as the game progresses. After you have equipped the sword, exit this area by crawling back out.
Begin to walk around the Forest and cutting grass with the sword and lifting up rocks and breaking them until you come up with 40 rupees. Then head over to the building with the red roof (it's in the northeastern part of the Forest - it is a shop). Purchase a Deku Shield and then equip it. By the way, you should be saving the game periodically, and at important times such as this one when you receive a new item. That being said, head to the eastern part of the Forest until you meet a child who is blocking your path. Talk to him and he should let you by (if he doesn't, make sure that you have equipped both the sword and your shield). After the child lets you by, you will encounter your first enemies. Practice on them with your sword - they are not difficult.
You will probably receive an item such as a Deku Stick for defeating them. To use an item like this, press Start and move to the menu that has the Deku Stick on it. Press any of the yellow "C" buttons (with the exception of the top one) to equip it. You can equip up to 3 different items with the "C" button in addition to the sword and shield. To use the items, simply push the corresponding "C" button and you will use the item. Here is yet another thing that I expect you to remember how to do - it will greatly facilitate future tasks that I will write about.
After defeating the enemies and collecting any items left behind, proceed east until you meet the Deku Tree. He will speak with you and then tell you to enter via his mouth....