das Glas
glass
A container made of glass that you drink from.
Stell die Gläser für die Gäste schon mal auf den Tisch.
Go ahead and put the glasses on the table for the guests.

glass / jar
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glass
A container made of glass that you drink from.
Stell die Gläser für die Gäste schon mal auf den Tisch.
Go ahead and put the glasses on the table for the guests.

The plural form 'die Gläser' almost always refers to drinking glasses (meaning m01). The material 'Glas' (glass) (m02) is uncountable and therefore has no plural.
Kannst du bitte noch zwei Gläser aus dem Schrank holen?
Could you please get two more glasses from the cupboard?
When 'Glas' (glass) refers to the material, it is uncountable and is often used without an article. It is also a common component of compound nouns such as 'Glastisch' (glass table), 'Glaswand' (glass wall), or 'Glasflasche' (glass bottle).
Die Tür hat einen Einsatz aus Glas.
The door has an insert made of glass.
As a quantity, 'ein Glas' (a glass) stands directly before the noun it describes, usually without an article. This structure is especially common with drinks and foods.
Zum Frühstück trinke ich immer ein Glas Orangensaft.
For breakfast, I always drink a glass of orange juice.
The contents reveal whether a drinking glass (m01) or a storage jar (m04) is meant. 'Ein Glas Wasser' (a glass of water) is a drinking glass, while 'ein Glas Marmelade' (a jar of jam) is a storage jar (a preserving jar).
Er bestellte ein Glas Bier.
He ordered a glass of beer.
cup
'das Glas' and 'die Tasse' can both be drinking vessels and can also refer to an amount, for example 'ein Glas Wasser' (a glass of water) or 'eine Tasse Tee' (a cup of tea). The most important difference is the typical shape and use. A 'Glas' is usually transparent, has no handle, and is often used for cold drinks. 'Glas' can also mean the material glass, for example in windows or bottles. A 'Tasse' usually has a handle and is especially used for hot drinks such as coffee or tea. Learners often confuse the words because you can drink from both. As a practical rule: water or juice is more likely to be in a 'Glas', coffee or tea more likely in a 'Tasse'.

Zum Abendessen trinkt Mehmet ein Glas Wasser.
Mehmet drinks a glass of water with dinner.
Frau Kaya stellt ihre Tasse Kaffee auf den Schreibtisch.
Ms. Kaya puts her cup of coffee on the desk.