"Furthermore" is similar to "in addition." Use this to add more information in your sentence. It's a little formal, but you can use it when speaking English.
Sometimes, the second part of the sentence that follows "furthermore" contains information more pertinent (important) than the first part.
examples
Reading is a good way to learn new vocabulary words; furthermore, it can improve your ability to spell words correctly.
Grilling makes meat taste really good; furthermore, it allows fatty juices to drain away from the meat.
Homelessness produces intense feelings of despair in those who don't have a place to live; furthermore, it produces feelings of guilt among people who are not homeless.
Religion offers people an opportunity to reflect on their personal existence; furthermore, it brings communities together in a spirit of peace and cooperation.
The use of fire by early humankind made cold climates more inhabitable; furthermore, it made people more productive by lengthening the number of hours that people could do work.
Driving while distracted increases your chances of getting into an accident; furthermore, it endangers the lives of other drivers.
Recycling is an easy way to conserve natural resources; furthermore, it can help reduce garbage disposal costs.
"What's more" is an idiomatic form of "furthermore." In each of the sentences above, you could substitute "what's more."
