It's important when casting to remember that you don't assign prepared spells to the casting slots in advance. Essentially, they're spell points...
So, at level 1, you've got two 1st level casting slots. (No increase for high Wis, either.)
You can have ready to cast 1+WisMod spells of levels 1+. Usually, this means 3 or 4 total for a 1st level caster. So, let's say, cure wounds, bless, healing word, command.
Until you cast, the spell isn't using the slot. So, if you need to heal someone across the room, you use healing word. If they're next to you, Cure Wounds. Or, if only one badguy is left, and you can't stop him, you can try Command: grovel ...
And cantrips are different... they are at-will... cast every round if desired... sacred flame is great.