Please help me with this difficult math question

I honestly don't even know where to start.

Find an equation to calculate the sum of the first "n" intergers. Give 2 or 3 examples to show that the equation works.
Please show work.

I don't even know what it is asking.

Series is 1,2,3,4,5,6,7............n
a = 1
d = 1
Sum = [2a+(n-1)d]*n/2
Sum = [2+(n-1)]*n/2
Sum = (n+1)*n/2
Example Sum to 3 terms = 4*3/2 = 6
Check 1+2+3 = 6
Sum to 5 terms = 6*5/2 = 15
Check 1+2+3+4+5 = 15
Sum to 7 terms = 8*7/2 = 28
Check !+2+3+4+5+6+7 = 28

Sum of the first "n" integers...is like the sum of an arithmetic progression with the increment (common ratio) of 1

Sn = (a1 + an) * n/2

First (?) n integers is quite an ambiguous request...
- infinity ....-3, -2 , -1 , 0 , 1 , 2 , 3......infinity

Where are the first? from "- infinity" up?