That was a question i made to my teacher when i was a little boy. "Há" comes from the verb "haver" that means "to exist" and due to the imense capacity of expression that the english have, it can sometimes mean "have" and in this case "there be" and it's variants. About "a", it is a feminine definite article or "artigo definido feminino" in portuguese. The key to never get lost by their sound is to pay attention in the context. Let's make both situation and see which is more reasonable (the word with " " is the wrong one): Há suco no copo / vs / "A" suco no copo. OK! Há suco no copo seems ok, since it means literally "There exists juice in the cup". What about the other one? "A suco" literaly means "the juice", but there is a small error..... "Suco" is a masculine subjective, i mean, if i want to say "the juice" i gotta say "O Suco", not "A suco", hence the usage of a in this case is totally busted =w=But to be honest we brazilians don't say "Há suco no copo" or "Há uma garota alí" which mean "there is a girl". I would say "tem uma garota alí" or "tem suco no copo", THAT is alot like brazilian! Peace man~
I find it difficult to understand the meaning of the verb 'haver'. There is not a very consistent translation of the verb 'haver' on google translate (using the Portuguese conjugations supplied by verbix.com:
Eu hei = I will
Tu hás = Thou shalt (which sounds like English spoken in medieval times)
Você há = You there
Ele há = He has
Nós havemos = We are we ??? (Google's translation doesn't make much sense)
Eles hão = They will
Has anyone got any tips on the meaning(s) of haver and when to use them?
The most common usage of the verb «haver» is the 3rd-person singular conjugation of the verb in the various tenses: «Há uma borboleta aí.» = "There is a butterfly there," «Há muitos pares de meias em cima da cama.» = "There are many pairs of socks on top of the bed," «Havia muita gente lá.» = "There were lots of people there," «Apenas houve um freguês ao meio-dia.» = "There was only one client at noon," «Haverá uma tempestade de neve este fim-de-semana.» = "There will be a blizzard this weekend." As you can see, when used in this way (in the 3rd-person singular conjugation), the verb «haver» translates to "to be there" (or "there to be" in the correct order) in English. Note, also, that both "there is" and "there are" translate to the singular «há».
Then, you might encounter another construction: conjugation of «haver» + «-» (hyphen/hífen) + «de» (literally "of"). It looks something like this: «(Eu) Hei-de ir ao mercado mais logo.» = "I will go to the market later," «(Tu) Hás-de fazer isso para mim.» = "You will do that for me," «(Ele/Ela/Você) Há-de receber muitas prendas este ano.» = "He/She/You will have many presents this year," «(Nós) Havemos-de/Hemos-de prestar atenção.» = "We will pay attention," «(Vós) Haveis-de/Heis-de procurar uma solução.» = "You will look for a solution," and «(Eles/Elas/Vocês) Hão-de encontrar a receita.» = "They/You will find the recipe." Note that these conjugations are all in the present tense in Portuguese but express a future sense. Hope this helps.