What we know about God from the book of Hebrews

"God" The first word of the book.  God is presumed and exists  Heb 1:1

God acted in different times of history.

Heb 1:1 God, who at sundry times and in divers manners spake in time past unto the fathers by the prophets,
Heb 1:2 Hath in these last days spoken unto us by his Son, whom he hath appointed heir of all things, by whom also he made the worlds;