The term input is referring to ‘x’ and the output is ‘y’.
To find the pattern you need to look at what x is to see the relationship to y.
An example is
(x,y)
0,2
1,3
2,4
3,5
4,6
5,7
When looking at the relationship in these numbers you can see that every time you add two to whatever x is to get y.
The equation for this line would be y=x+2