Yeah, I know Alex sucks. SO slope is the change in Y over x. So to find slope for ex. is lets use points (8,4) and (6,5) the equation to find slope is Y2-Y1 over X2-X1 or Y2-Y1 / X2-X1 and that basically the y's on the points you have. In this case it will be 4 and 5 since y always comes second or after the x. What I like to do is this X1(8), Y1(4) and X2(6), Y2(5). After you have that set up you just put them in the equation it will be 5-4/6-8 which is -1/2 use calculator. So Y is the y-axis and X is the x-axis.
Function is when every input(x) has only one output(y) . For example if we have the table
X,1 , 4 , 5, 9, 10 this is not a function because the -3 has both 9 and 10 for an output.
Y,2, 6 ,6, -3 , -3
A function will look more like this
1 2 3 4 5 6
2 4 6 8 10 12 every output has only one input
I recommend to watch Brian McLogan on youtu he can really help. Just search anything then his name. Or even Function then his name he explains it really well.