I am having trouble with how to determine whether the relation is a function. I don’t understand what would make it a function or not a function.

I am having trouble with how to determine whether the relation is a function.  I don’t understand what would make it a function or not a function.  I can see that the domain is increasing from -3 all the way to 10.  But the range keeps throwing me off.  The range jumps from -8 to 6 then to -5 so its confusing me.  Online study sucks.  Maybe you can explain better as to why it is a function or is not a function for me so I can better understand it.  Thanks!
{(-3, -8), (3, 6), (5, -5), (7, -6), (10, 6)}
 
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