Hello there! Good question. In this context, "be held" does have the same meaning as "happen/take place/occur." There is only a slight difference in usage... "What time is the party going to happen" is more informal then "When is the party going to take place/occur/be held." So use "happen" amongst friends and family, and perhaps use the others in professional settings. Other example: "The jewels will be held at Singham Palace until future notice."

"Held" is the past participle of the verb 'hold'. The verb "hold" can mean many things, depending on the phrase that it is in. When the object of the word 'hold' is an event ( hold a party, hold a conference, hold a tournament) , it means to organise or be the host of the event. This would translate into Portuguese as 'realizar' , I think. Note that ''What time is the party going to be held?'' is in the passive voice. What time is the party going to be held? [passive] What time are xxxx going to hold the party? [active] In this case, xxxx are the hosts of the party, or the people who are organising this event. For example, you could say "The winter Olympics will be held in Korea" instead of saying "They [meaning the organisers] will hold the winter Olympics in Korea".