The mean, median and mode are three types of averages which you will be asked about in your GCSE maths exam.
The best way to learn maths is by by doing it or at least running through examples.
E.g. Given the following numbers work out the mean, mode and median:
1, 2, 3, 4, 5, 5, 8
Mean: To calculate the mean you add up all the numbers and divide them by how many numbers there are in the sequence.
So here: Mean = (1+2+3+4+5+5+8) / 7 = 4
Here there are 7 numbers so as shown above we divide the total of the numbers by 7.
Mode: To find the mode we simply find the number which appears the most times in sequence. So here the answer is 5 as it appears twice whereas all the other numbers only appear one time.
Median: To find the median we find the number which occurs in the middle of the sequence:
1, 2, 3, 4, 5, 5, 8 Here the answer is 4. This is because there are seven numbers in the sequence and 4 is the number which occurs in the middle.
A harder example:
1, 2, 3, 4, 5, 5, 8, 9
Here there are eight numbers in the sequence. So there is no single middle value. Here the two middle values are 4 and 5. So to calculate the median when this occurs (when there is an even amount of numbers in sequence), we find the number in between the two middle values. So the number in between 4 and 5 is 4.5 and this is our answer.