Because - zato. Jer, zbog, usled is mainly - couse of something I did not make it couse of you - Nisam uspela zbog tebe. I did not go there couse i had no time - Nisam isla tamo jer nisam imala vremena.

Because - zato .I always translate with this word

In general, there's no difference in meaning, there's only the difference in registers (formal/informal speech) and the required verb/noun form that goes with the conjuction. Zbog, zato and jer are probably the most common expressions. You use zbog with nouns in genitive case (Zbog kiše ne mogu da izađem napolje - or - Ne mogu da izađem napolje zbog kiše). With verbs, you use expressions zbog toga što and zato što (e.g. Ne mogu da izađem napolje zbog toga što pada kiša / Zbog toga što pada kiša, ne mogu da izađem napolje; you would use zato što in the same way). Jer is used very often, but only with verbs and never at the beginning of a sentence (Pozvao sam roditelje jer je bilo kasno; NOT: Jer je bilo kasno, pozvao sam roditelje - this just can't be said). Usled is usually used in formal writing, you would never say that to your friends (e.g. in the papers - Utakmica je prekinuta usled lošeg vremena). There's a ton of other expressions, but I think this is enough for beginning. And do tell me if you can't understand the examples, I'll translate them into English if you want me to...