User Portlet User Portlet

What is a good web series that covers almost EVERYTHING Mathematicia? I cant find a good one.
I dont know if i just am not doing Summation right, or if i am incorrectly entering Mathematica's Syntax, either way i typed in Sum[1/n, {n = 1, 10}]expecting to get something close to 2 (closer to 2 the higher the last number is) and...
Thank you everyone i got it figured out, now i have another question, i forgot to mention i am new to mathemeticia, i got it yesterday. how would I tell mathemeticia in NSolve[(x^2) + (y^2) == z^2] to only list natural numbers