Some glass can break in a microwave if the glass is not made to take the heat of the microwave and is not microwave safe.
The non microwave safe glass could have tiny air bubbles in it which can expand during the microwave and heating process.
That then leads to the glass breaking in the microwave.
A lot of glass is okay to microwave and I've microwaved glass bowls and ceramic mugs without a problem even though they do not have a label saying microwave safe.
If you place a glass dish in the microwave and it begins to get too hot then it is likely not microwave safe and could break.
But if the glass dish gets partly warm then it's usually okay to microwave.
Most microwave safe dishes will be stamped on the bottom saying that it's microwave safe.