to produce bubbles:
Heat the cheese until it bubbles.
The cola bubbled up when I unscrewed the lid.
to make the sound that water makes when it boils
The water was bubbling away on the stove.
3 also bubble over
to be excited
Mary was bubbling over with excitement.
4 also bubble away/up
if a feeling or activity bubbles, it continues to exist:
Resentment was still bubbling inside her.
Speculation has been bubbling away for months that he plans to resign.