During the game you'll get the chance to power up your tools. Powered up tools will make working on your farm a lot easier by saving you time and energy.
The Watering Can is given to you by Daisy at the beginning of the game. It allows you to water one square/plant at a time. Eventually you can upgrade your Watering Can to the Sprinkler. The Sprinkler can be bought from Bill at the Tool Shop for 2000G. It seems to appear at Bill's shop the next day after you have shipped your 100th item. The latest date that the Sprinkler is available is the 25th of Spring in the first year. Some have reported it being for sale as early as the 12th of Spring. The Sprinkler allow you to water a 3x3 grid of plants.
The Hoe allows you to cultivate the ground in order to plant seeds. Both grass and crop seeds need to be sprinkled on land that has been plowed up by the Hoe. The Hoe also allows you to shape your crop patches. While using the Hoe to plow the ground, it will eventually break on you, usually in the first year's Spring or Summer. After it breaks go visit Bill at his Tool Shop. He will repair it into the Super Hoe for you. Return for it after 3 days. The Super Hoe will allow you to plow up a long strip of 6 squares.
You can also get the Hoe upgraded as a birthday gift. Bill will come by on your birthday and ask if you would like your Hoe or your Sickle upgraded. Return to his shop 3 days later to pick up your Super Hoe
You normally use the Hammer to break rocks and broken fences. The small rocks can be destroyed with one hit and the large rocks need 6 hits to shatter. It's hard work destroying those large rocks! Once you have your house expanded the first time by Ken (you'll need 30000G and 300 Wood), return back to his shop and he'll give you the Super Hammer. Now you will be able to destroy the large rocks in one hit.
On your birthday (which the date you set at the beginning of the game) Bill will come by and offer to power up one of your tools. The Sickle normally only cuts one square of grass at a time, but after you power it up the Super Sickle will cut 9 squares of grass at once. After you tell Will that you want your Sickle upgraded, return to his shop 3 days later to pick it up.
The Super Ax is one of the last super tools you'll receive. You need to become friends with Daisy, the Florist shopkeeper. Talk to her on Sundays when she's out in the Town Square and choose the "Talk" option when you go to buy seeds from her. She'll start warming up to you when instead of saying "Water Daily" when you talk to her in her shop, she'll start to say "Hi! What'll it be today? I highly recommend everything". One day Daisy will eventually tell you that she found the Ax that her dad used when he was a woodcutter. She then will give you the Super Ax.