From the Player's Handbook, Chapter 10:
Many spells specify that a target can make a saving
throw to avoid some or all of a spell’s effects. The spell
specifies the ability that the target uses for the save and
what happens on a success or failure.
The DC to resist one of your spells equals 8 + your
spellcasting ability modifier + your proficiency bonus +
any special modifiers.
The bold part makes me think that only some spells need the targets to roll a saving throw, like Burning Hands.
A creature takes 3d6 fire damage on a failed save, or half as much
damage on a successful one.
But some spells don't say any of that, like Scorching Ray.
You create three rays of fire and hurl them at targets
within range. You can hurl them at one target or several.
Make a ranged spell attack for each ray. On a hit, the
target takes 2d6 fire damage.
At Higher Levels. When you cast this spell using a
spell slot of 3rd level or higher, you create one additional
ray for each slot level above 2nd.
Should the target(s) roll a saving throw for spells like Scorching Ray?