Well, very early in the game Link gets a wooden sword and learns how to use it against a scarecrow in Taoru Village. This is the combat learning process. To think that Link would need to learn how to use his shield after obviously leaving his town and being who knows where is pretty ridiculous. This sequence is something else, and I'm not saying that the Goron is Link's enemy necessarily (it certainly seems that way, at least to an extent), since it could be some sort of proving your worth ordeal, but it's late enough in the game to assume that Link already knows how to block, especially if you already knew he trained with the scarecrow.