all plants start with two leaves called the cotyledons, I believe, and it is possible to start to recognise them, especially when the second pair of leaves arrive, which look different from the cotyledons, and look like what will follow. I am a beginner also, but find the following website good, as it shows the plants in the early stages. Like one of the others said, watch all your seedlings/weeds grow, and learn what they are, and enjoy
http://www.dgsgardening.btinternet.co.uk/index.htm