A volcano is a kind of mountain that sometimes erupts. When a volcano erupts, it kind of explodes. Smoke and ash come out of it. Hot liquid rock, called lava, might also come out of it.
The word "erupt" mostly describes volcanos. There are some situations in which you can say that a person erupted. When a person erupts, they suddenly start to make a loud noise like yelling or laughing:
Everyone standing around erupted in laughter when he told us that.
There've been a few occasions when Murray has suddenly erupted in anger at us, but it's certainly not common.