I'm pretty new to DnD and I'm playing with a group who is also just starting so I'd just like something clarified.

I'm not entirely sure I understand what the PHB is telling me about spell attacks. Say I'm a wizard who's casting Fire Bolt (I could also be a Cleric casting Inflict Wounds or what-have-you), the spell itself doesn't say anything about making an attack roll or the enemy making a saving throw. So do I make an attack roll and then add in my INT mod + proficiency bonus? Or does the target have to make a saving throw against a DC of 8+ my INT mod + proficiency bonus?

And assuming I hit: do I add my INT mod + proficiency bonus to the damage?