A frequency table lists each group of data and the number of occurrences for each category of data. The groups are usually categories (such as car color), intervals (as seen on the right), or values (like number of cars) that will be recorded in the first column. If the classes are numerical, then they need to be listed in ascending order. After making the first column, you record the tallies for each class in the second column (note that this second column can be omitted). Then you add up all the tallies and put the final frequency in the third column.
A frequency table is useful to show how often a certain value (or set of values) occurs within a data set. If the data is ordinal, then the table frequencies can demonstrate central tendency, mode, symmetry, and spread.
Frequency tables can be misleading if the intervals are abused. For example, the intervals could be made with gaps or overlaps.
A very basic definition and a few simple examples can be found here. A guide to making a frequency table is given in example 1 on this site. On the Science Kids‘ website there is a game that demonstrates how to make a frequency table.