Calculating the Percentage of Cells in a Range that Contain a Specified Stri

i am sort of new to Excel, and im planning on using that formula for some spread sheets i am creating. However, what is the reason for the ,B1? i dont understand what each string in columb b means.

Problem:

We want to create a formula that searches List1 (cells A2:A9) for each string in column B and returns the percentage of cells containing that string.

Solution:

Use the COUNTIF and COUNTA functions in the following formula, and then apply percentage formatting to the cells:
=COUNTIF($A$2:$A$9,B2)/COUNTA($A$2:$A$9)

what i want to do is use this formula or alter this formula to help me out. I want it to give me a % of say one word through one column on all of my work sheet..i guess what im trying to ask is what is a string?