To find the mean of a set of numbers you add them all up and divide by the amount of numbers. For example, to find the mean of 2, 5, 1, 6, 4 add them up, (the answer is 18), then divide 18 by 6 since there are 6 numbers. The answer is 3, so the mean of this set of numbers is 3.
Finding the Median is simple, it's just the middle number. When you have the set 2, 5, 1, 6, 4 instead of just figuring it out like the Mean, you need to organize them (least to greatest) first. So it will be, 1, 2, 4, 5, 6... Now you just find the middle number (4)
Finding the mode is simple as well, the mode is the most common number in a set of numbers. So, in the set 2, 5, 1, 6, 4 there won't be a mode because there is just 1 of all the numbers, however when you add a 5 to the set of numbers, the mode will be 5 since there are 2 5s and 1 of everything else.
Finding the Range is a bit more tricky, to solve it you need to subtract the lowest number from the highest. And like the Median you need to organize the numbers in a set of numbers from least to greatest. So, instead of 2, 5, 1, 6, 4 it will be 1, 2, 4, 5, 6. To find the range just subtract 1 from 6, the answer is 5. So the range is 5.