In very simple words, and far from technicalities, the focal length is something like the scope of the objective. The higher the value, the more "zoomed in" the lens, so to speak. Please forgive me the purists, maybe it is not an orthodox explanation but many people understand it better that way. .
The longer the focal length, the more “zoom” the lens will have, and the less of the scene it will capture. The shorter the focal length, the more "far" things will look, say, but the framing or angle of view will be much wider instead
Shutter speed: the length of time the shutter remains open allowing light to enter.
At faster speeds, motion freezes, like a falling drop of water. With slow speeds you can capture the movement of objects being blurred.
ISO: A numerical standard that measures the sensitivity to light of an image sensor or film. At higher ISO the camera captures more light, at lower ISO less light.