Genesis is included in the Torah, which is the first five books of the Bible. Joshua 8:31 says that Moses wrote the Torah:
And there, in the presence of the people of Israel, he [Joshua] wrote on the stones a copy of the law [torah] of Moses, which he [Moses] had written. (ESV)
Moses is credited with writing Genesis but where did the information come from since he was born generations beyond ‘Adam’?