When you go down the way in the beginning, on your left you can find the place to fish.
A bit further down, on the right, there is a hollow trunk. Go through there!
Following the path further, you cross a bridge and find a fireplace with storage. From there, a way leeds strait forward to a cave, right to a place where you find firewood, bit left up to the mansion, left to the other side of the lake, where you find the fishing rod. There is more to discover but I think this should be fine for the beginning.