Key things you need to know:
A lot of vegetables do contain similar amounts of iron as meat does, but the iron from plants is not as easily absorbed by our bodies. Make sure you are drinking/eating foods which are high in vitamin C, as vitamin C helps with the absorption of iron. This can be as simple as drinking a glass of orange juice for breakfast.
Though despite this, iron deficiency has shown to be no more common in vegans/vegetarians than in meat eaters.
http://www.vrg.org/nutrition/iron.htm
B12 is only found in very low amounts in some plants. If you're vegetarian then you will be getting sufficient amounts of B12 from eggs/dairy. Though vegans will need to eat foods such as mock meat, soy milk etc. which are fortified with B12 or take supplements.
Though vegetables and fruit contain a lot of useful nutrients, they do not contain large amounts of protein. Good protein foods are legumes such as chickpeas and lentils, also soy products like tofu. Here is a good list of how much protein is in different foods:
http://www.vegparadise.com/protein.html
Honestly you don't have too much to worry about. You will easily be able to get everything you need from non-meat sources
I went veg when I was 12 (8 years ago) with very little education about nutrients and I am perfectly healthy.
