Extensive reading fills the mind with information and ideas which inspire and provide for further thought and lead to new ideas. A "full" mind is obviously better than an empty, or ignorant, one.
By "conference" Bacon evidently means conversation. Conversing with many people, and with many different kinds of people, will make a man, or woman, sophisticated, versatile, and adaptable to varying situations and personalities. Such a person is often said to be able to "think on his feet."
Writing makes an exact man because writing forces one to think about what he believes and what he wants to communicate. It also develops the habit of always trying to find the right word. Sometimes we may surprise ourselves by coming up with words we know but didn't know we knew. Writing and thinking go hand in hand. Gustav Flaubert stressed the importance of using the right word, le mot juste. And the great German writer Thomas Mann once said:
A writer is somebody for whom writing is more difficult than it is for other people.
There is nothing in the world more educational than acquiring the habit of writing every day. Anne Frank's diary is a good model for young people to follow. Many famous writers kept journals. Henry David Thoreau was one of them. He wrote millions of words about his thoughts, feelings, observations, reading--anything he felt like writing about.
Bacon's statement in his essay "On Studies" is one of his most often quoted and one of his many pithy and profound observations. All writers would agree with him.