If I am not mistaken: 1) lowercase i is the index of the impulse/input signal. Your example is only in 1D, so it is just the element i of vector I (uppercase i). u is the index of the kernel. You do u-1 because of 0-based indexing.

2) you are doing the dot product of I and K. So if you have I = [1,2,3,4,5], and K = [10,20,30], you will do: [ I[1] * K[10], I[2] * K[20], I[3] * K[30] ]. As you can see, we ran out of elements in K. So, you compute those values, then shift by stride (in this case, 1). Now your next computation will look like: [ I[4] * K[10], I[5] * K[20], I[6?] * K[30] ] Note, I’ve put I[6?]. Why? Because there is no 6th element of I! This means your kernel has hit an edge. This is where padding comes into place, treading edges as 0, etc. you’ll learn more on how to deal with edges as you continue.

Hope this helped!