Definition of "Haver" - (verb) - to have, posses, be. Full conjugation here
Seems pretty simple right? Not really. Seems like the colloquial usage of the verb has changed, particularly in Brazilian Portuguese. After some thorough Internet research (I think), I've aggregated the various uses of the verb.
Usage #1 - Concept of "exist". Literal translation of "there is" / "there are".
When haver is used in the 3rd person, a majority of the time it means "there is" / "there are".
The use of the third-person "haver" conjugation is impersonal; in other words there is no explicit subject in the sentence.
Examples:
Há - Present Indicative Tense - Third Person
Há um garoto aqui. --> There is a boy here
"Há um livro na escrivaninha?" "Não, não há." --> Is there a book on the desk? No there is not.
Há um pouco de verdade no que ele está dizendo. --> There is a certain amount of truth in what he is saying
Havia - Imperfect Indicative Tense - Third Person
Havia um tempo em que havia uma ponte aqui. --> One time there was a bridge here
Havia uma grande audiência no concerto. --> There was a large audience at the concert
Other 3rd person forms include:
houve - preterite indicative - there was / there were
haverá - furute - there will be
tinha havido - present perfect - there had been
haja - present subjunctive - there is / are
houvesse - imperfect subjective - there was / were
houver - future subjunctive - there will be
haveria - conditional - there would be
3rd person form examples:
É possível que haja uma reunião no mês que vem --> It is possible that there will be a meeting next month
Se houver alhum problema, lique para este número --> If there is any problem, call this number
Houve um debate acalorado no Senado --> There was a headed debate in the Senate
Havia mas de 30.000 pessoas no jogo de ontem --> There were more than 30,000 people at yesterday's game.
Deve haver uma soluçao --> There must be a solution
In colloquial spoken Brazilian Portuguese, any third person use of haver (when it means "to exist") can be substituted with the ver "ter".
Vai ter churrasco no domingo --> There's going to be a barbecue on Sunday
Tem leite na geladeira --> There's milk in the fridge
Tinha uma viatura da polícia parada na frente da casa deles --> There was a police car stopped outside their house
Usage #2 - Concept of "for", denoting a period of time that started in the past and continues in the present
When the third person present indicative tense of haver is used ("há") combined with other verbs in the indicative present tense, the construction "for" is created:
Moramos no Rio há cinco anos --> We've been living in Rio for five years
Você está aqui há muito tempo? --> Have you been here long?
When "há" is combined with other verbs in the indicative preterite, the meaning is changed to "ago"
Eles mudaram para os EUA há seis meses --> They moved to the USA six months ago
A empresa foi fundada há meio século --> The company was founded half a century ago
O escritor morreu há quinze anos --> The writer died fifteen years avon
Recebemos a noticia há alguns minutos --> We got the news a few minutes ago
Usage #3 - Haver + de + infinitive verb.
Using haver + de + infinitive can express a future action. From what I can gather, this form is rarely used today in spoken Brazilian Portuguese, however, it does exist. Here are some examples.
Examples taken from Modern Brazilian Portuguese Grammar by John Whitlam - ISBN: 0-203-84392-4
