ISO stands for International Standards Organization and is a number given to a film that reflects its sensitivity to light. The higher the number the less light you need to take a photo. The lower the ISO the more vibrant and saturated the colour reproduction is. So if you are taking pictures of brightly coloured flowers on a sunny day, try 100 speed films. On the other hand if you are taking pictures of your child's Christmas concert in the school gym, try 400.
Every manufacturer bases their film on different colours of the spectrum.
This means that colour is a little more prominent than the others. Reds and oranges are warm colours giving you that warm and fuzzy feeling, greens offer lush vegetation, and blues are usually considered cold technical colours. If you have trouble remembering what colour a film is based on, look at the box. Film is usually packaged in colours similar to it's base colour. Disregarding TV ads and marketing promotions can open up many more choices for you.