For the first time in my life I have decided to try and get healthy and fit, but I don't have a clue where to start, I have been given two 7.5 kg one arm dumbells so i thought maybe using these mixed with sit Ups and running might help. Would this be enough? Do i need to eat/avoid certain foods? I don't want to have huge muscles just toned and not get out of breath when i walk up stairs