I will assume you are dealing with data analysis or statistics.
Lets assume you have a sample x1. x2, .., xn of measurements of something,
to be concrete suppose these to be the heights of you class mates in inches.
By the "mean" we normally the arithmentic mean which is the sum of the
measurements divided by the number of measurements:
mean(x1, x2, .., xn) =(x1 + x2 + .. + xn)/n
It is a measure of the central tendency of the data set, sort of a typical
value for the x's.
By the mode of a data set like the one we are discussing we mean the
value that occurs most ofter. So if our set were {61, 62, 60, 61, 57}
the mode would be 61. The mode is another way of indicating the
central tendency of a data set, but is more appropriate to categorical data
rather than the numeric (interval) data for which the mean is more appropriate.
The range is the difference between the largest and the smallest values
in a sample, it is an indicator of the spread of the data.
RonL