How to use these in spanish?

Im trying to better understand prefixes (if that is what they re called) in spanish when you have "al" in front of a work like al fin what does that mean. also when you use "se" por ejemplo se cayo what does the "se" do? and on an ending of a verb like saltar you add "se" at the end to make it saltarse how does that change the word ??? and also when you have the ismo and cito and you want to change a word using those, are you only allowed to used verbs??? I know this isnt in order i cant better explain myself. gracias mil veces!