Film and shutter speed.
It seems odd to talk about 'film speed' when digital cameras dont have film. However they do have a 'sensitivity' feature. This is usually labelled as ISO and typically goes from 68 up to 800.
Shutter speed is the ammount of time that the light hits the sensor and is usually measured in fractions of a second. The faster the shutter speed, the more 'frozen' the action will be.
Slower shutter speeds allow more light in but if you have shaky hands your photograph might be ruined. For landscape sunsets a slow speed is needed, so photographers use tripods so that they don't cause camera shake while taking the shot.
Next lesson: Framing a shot