Hi! When you say "te gusta" it means "you like it" but with a singular "you" : you are talking to only one person. When you say "os gusta" you're talking to the "plural" "you". "Te" stands for "tu" "os" stands for "vosotros" "El" means "the" ("el chico"= "the guy" )and "le " is two articles put together : "a" ("to")+ "él" ("him") = le. So when you are saying "le gustaria" it is a passive form : instead of saying "he would like it" you're actually saying "this would be liked by him". In spanish you use that passive form very often. I hope I made it more clear to you!

te gusta = tu aimes, mais la traduction plus proche à cette construction serait: il te plaît le gusta = il lui plaît, ou bien il vous plaît (formel singulier) os gusta = il vous plaît. (seulement "vous" pluriel) les gusta = il leur plaît ou bien il vous plaît (formel pluriel)

The answer for the pronouns te / os / le is very simple, the person they refer to: te = segunda persona del singular (tú = you) le = tercera persona del singular (él = he/she) os = segunda persona del plural (vosotros = you) All of them are "pronombres personales átonos", which develop the function of direct or indirect object in a sentence. On the other hand, "él" es a "pronombre personal tónico" which act as the subject (or "atributo") of the sentence..