Joshua son of Nun is a person in the Bible. Joshua is used as a general against Amalek after Amalek attacks the Israelites. When Moses goes up to Biblical Mount Sinai to get the Torah from God, Joshua stays at the bottom of the mountain waiting for Moses to come back. He doesn't realise that the people are worshiping a Golden Calf as an idol until after Moses tells him.
When two people named Eldad and Medad become prophets, Joshua is annoyed because he thinks only Moses should be a prophet though Moses tells Joshua that if it were up to him every Israelite would be a prophet.
Joshua, it turns out was once named Hosea but then Moses sends him as one of Twelve spies to Canaan after first renaming him Joshua. Ten of the spies try to convince the Israelites that it would be better to go back to being slaves in Egypt than enter the Promised Land because if they tried to conquer Canaan they'd get killed. Joshua and Caleb said that if they came to the Promised Land, God would make sure they would survive against their enemies just like He had saved them from Egypt.
When Moses dies, he, at the command of God, appoints Joshua leader of the Israelites. Joshua mourns Moses for many months after his death but then God commands Joshua to conquer Canaan. Joshua enters the Promised Land as a general kills 39 kings and manages to take over most of the country. He then divides the land among the Twelve Tribes of Israel and then dies. There is a book in the Bible named after him called the Book of Joshua.