Ter vs. haver
In Portuguese, both ter and haver can be used to express existence, similar to the English there is or there are. However, their usage differs significantly based on formality and specific meaning. Ter is also the primary verb for possession, a role haver does not have.
Ter
A1The verb ter is extremely common and its primary meaning is to have in the sense of possession. In informal spoken Portuguese, especially in Brazil, it is frequently used as a substitute for haver to mean there is or there are. It is also used as an auxiliary verb to form perfect tenses.
Eu tenho um cachorro e dois gatos.
(I have a dog and two cats.)
Ela tem cabelo comprido e loiro.
(She has long, blond hair.)
Nós não temos tempo para isso agora.
(We don't have time for this now.)
Tem muita gente na fila do cinema.
(There are a lot of people in the movie theater line.)
Não tem leite na geladeira.
(There is no milk in the fridge.)
Eu tenho estudado português todos os dias.
(I have been studying Portuguese every day.)
Haver
A2The verb haver is the more formal and grammatically standard way to express existence (there is/are). When used this way, it is an impersonal verb and always remains in the third-person singular form. It is also used to indicate elapsed time, to mean to occur or to happen, and as a formal auxiliary verb.
Há muitos problemas a serem resolvidos.
(There are many problems to be solved.)
Havia poucas pessoas na reunião.
(There were few people at the meeting.)
Haverá uma conferência na próxima semana.
(There will be a conference next week.)
Houve um acidente grave na rodovia.
(A serious accident occurred on the highway.)
Eu moro em Lisboa há dez anos.
(I have been living in Lisbon for ten years.)
Ele havia chegado antes de todos.
(He had arrived before everyone else.)
Summary
To put it simply: for possession (to own), always use ter. To express existence (there is/are), haver is the formal and grammatically correct choice (always in the singular form), while ter is the common, informal alternative. For talking about elapsed time (e.g., five years ago), only haver (as há) is used. As an auxiliary verb, ter is used in everyday language, whereas haver is reserved for formal or literary contexts.