Chamar vs. ligar
In Portuguese, both chamar and ligar can be translated as "to call", but they are used in completely different situations and are not interchangeable in this context. The key difference lies in whether you are calling someone over or calling them on the phone.
Chamar
A1The word chamar means to call in the sense of getting someone's attention, summoning them, or calling out their name. It is used for calling a person directly, not using a telephone.
Vou chamar o garçom para pedir a conta.
(I'm going to call the waiter to ask for the bill.)
A professora chamou o aluno pelo nome.
(The teacher called the student by his name.)
Por favor, chame um táxi para mim.
(Please, call a taxi for me.)
Ela ouviu alguém chamar por socorro.
(She heard someone call for help.)
Minha mãe me chamou para o jantar.
(My mother called me for dinner.)
Isso é o que eu chamo de um bom amigo.
(This is what I call a good friend.)
Ligar
A2The word ligar specifically means to call on the telephone or via a similar communication device. It is exclusively used for making phone calls. It also has other meanings like to turn on or to connect.
Eu preciso ligar para os meus pais esta noite.
(I need to call my parents tonight.)
Você pode me ligar de volta em cinco minutos?
(Can you call me back in five minutes?)
Ela me ligou ontem para confirmar o encontro.
(She called me yesterday to confirm the meeting.)
Para quem você está tentando ligar?
(Who are you trying to call?)
É muito caro ligar para números internacionais.
(It is very expensive to call international numbers.)
Não se esqueça de ligar a televisão para ver o jogo.
(Don't forget to turn on the television to watch the game.)
Summary
In short, use ligar when you are making a phone call. Use chamar when you are calling out to a person to get their attention, summon them, or call them by name. If a telephone is involved, the correct verb is always ligar.