basically:
llegar=arrive
venir=come
LLEGAR
--change from position a place from another place:
cuando lleguemos a casa, cenaremos.=when we arrive at home, we'll eat dinner.(we are not there so we "lleguaremos")
--- Achieve a particular goal, especially a position or profession:: ese chico llegará a presidente.=that boy will become the president.
-- to achieve or manage to do something: el llegó a reunir más de cien obras de arte.=he managed to gather more than one hundred works of art.
VENIR
--Go or move to where the speaker is: When will you come and see us? Maybe I'll go next month.= ¿Cuándo vendrás a vernos? A lo mejor iré el mes que viene.
---Getting to the place where the speaker is,to stay in it::The carpenter hasn't come yet= todavía no ha venido el carpintero.
---Come from a place: This chocolate comes from Switzerland=este chocolate viene de Suiza.
there are more examples but I can't remeber now....XD