Each class has what's called a Hit Die which determines how much HP a character accrues per level. At level 1, the character gets (typically) their full Hit Die plus their Constituion (Con) modifier ((##-10)/2, so 8 is -1, 14 is 2, etc). From there, Hit Die can be rolled as the character levels up or you can take the average for the HD, and add Con to that. So in this case, they're suggesting that Caesar, a 10th level Fighter (d10 hit die) would have on average 60HP total, though this would require them to have 'rolled' their level 1 HP pool (average of 5, plus a Con modifier of 1)