Theory:

The data we receive is raw; that is, it is unorganized data.
 
To make the unorganized data understandable, we tabulate the data received in tabular columns or bar graphs.
 
Sections of a tabular column:
 
We tabulate data under the columns Variable/Class, Tally marks and Frequency.
 
Variable/Class:
 
It consists of the unique type of entries in a set of unorganized data. In case of numerical variables, it is recommended to arrange the entries in ascending or descending orders. Ordering of data enhances the understandability of the tabular column formed.
 
Tally marks:
 
Vertical line(s) marked against each entry under the column 'Variable/Class'. Tally marks tells us the number of times each entry repeats itself in that set of data.
 
Frequency:
 
The numerical representation of the number of times an entry repeats itself in that set of data.
 
Let us look at a sample tabular column and analyze in detail.
 
The colours of pencils Vinod has:
 
Colour
Tally marks
Frequency
Blue
1235_2.svg
\(3\)
Green
1235_1.svg
\(2\)
Red
1235_4.svg
\(5\)
 
From the table given above, the 'Variable' is the different colours of pencils that Vinod has.
 
So, Vinod has blue, green, red pencils. So, these \(3\) colours are the three unique entries.
 
The number of pencils of each colour is given by using both tally marks and numerical representation.