'i' is an integer, index value. For the sake of the example, let's say i = 4.
t(i) is the 4th value stored in 't'.
t > t(i)-0.3 produces a logical vector of 1s and 0s the same size as 't'. It contains 1s whenever the value of t is greater than the 4th t plus 0.03.
So, if t = [0 1 2 3 4 5 6 7] and i = 4, the logical vector would be [0 0 0 1 1 1 1 1].
find() returns the index values that are true. so, find([0 0 0 1 1 1 1 1]) would return [4,5,6,7,8].
x([4,5,6,7,8]) looks at the fourth, fifith, sixth, seventh, and eighth values of 'x'.
To summarize, that line pulls out a subsection of 'x' based on the values of 't'.
