“so he gets the player location, subtracts it from the location of the sphere”
When we subtract a vector from other then we get a vector which have some magnitude and direction and when we normalize this vector we make the magnitude of vector to be 1 and keeps the direction of vector.
“Normalize” in vectors means to change the vector so that it points in the same direction (think of that line from the origin) but its length is one.
In tutorial, he is using the normalized vector (having direction and magnitude of one) , if the vector is not normalized then multiplying delta seconds output from tick event with not normalized vector will increase the value rapidly as distance between player and sphere will have some value more than one.