Vidro vs. copo
While English uses the single word "glass" for both the material and the container we drink from, Portuguese distinguishes between these two concepts using vidro and copo.
Vidro
A2This word refers to the hard, transparent material itself. You use vidro when talking about the substance, window panes, car windshields, or jars.
Cuidado, há pedaços de vidro no chão.
(Be careful, there are pieces of glass on the floor.)
A janela é feita de vidro à prova de balas.
(The window is made of bulletproof glass.)
Alguém quebrou o vidro do meu carro.
(Someone broke the glass of my car.)
Eu prefiro comprar leite em garrafas de vidro.
(I prefer to buy milk in glass bottles.)
Nós precisamos reciclar todo esse vidro.
(We need to recycle all this glass.)
Copo
A1This word refers strictly to the cup or vessel used for drinking. Even if a drinking cup is made of plastic or paper, it is still called a copo.
Você poderia me dar um copo de água?
(Could you give me a glass of water?)
O garçom deixou o copo cair da mesa.
(The waiter let the glass fall from the table.)
Em festas infantis, usamos copo de plástico.
(At children's parties, we use a plastic cup.)
Meu copo está vazio, eu quero mais suco.
(My glass is empty, I want more juice.)
Por favor, coloque gelo e limão no copo.
(Please put ice and lemon in the glass.)
Summary
To summarize, if you are talking about the substance or a window, use vidro. If you are talking about the object you hold to drink water or juice, use copo. Interestingly, you can have a copo (drinking vessel) made of vidro (material).