A well-kneaded dough can be recognised in a few different ways. Before kneading, the dough will be sticky and saggy, but after kneading, it will become more stretchy and hold its shape and not tear. What you are doing by kneading is developing the gluten in the dough. This gluten development facilitates the rising of the dough when it is baked by trapping gas released from yeast. Poke your dough with your finger - if it springs back, it has been well-kneaded.