Welcome to D&D! Lemme answer your question before I point out a few (small) errors on your sheet.
Spell saves are calculated by 8+CHA(because you're a sorcerer)+proficiency in this case, it should be 13. This stat is a number that enemies have to roll against to see if they are affected by your spell.
Your spell attack bonus should be CHA(Again, because sorcerers)+proficiency bonus, so it should be 5. This is added to your d20 roll when you roll to attack with a spell such as firebolt (I want to say this is the case for ray of frost and acid splash on your sheet but I can't be certain off the top of my head).
A few things to point out:
because you have 15 dex and daggers are finesse weapons, you can choose to use your dex instead of strength to calculate attack and damage. So attack could be a +4 and not a +1; damage could be 1d4+2 and not 1d4-1.
Your proficiencies are Stat+proficiency bonus, so insight should be WIS(-1)+Prof(+2) = +1 and religion should be INT(0) + Prof(+2) = 2.
Other than that, you did a great job for a newbie. Have fun in your games!