You form 'E4' first and get its cell value.
Then you form 'G4' and get its cell value.
And then do the same for 'F4'.
Then you form "Scores" namedtuple using the cell values of 'E4', 'G4' and 'F4'.
Then you check if that "Scores" namedtuple is a key in dictionary "dpos".
If it is, then get its value from "dpos" and paste in cell 'V4'; otherwise paste the "Unknown" string in 'V4'.
So, given:

Code:

pos_col_no = 'E'
alt_col_no = 'G'
ref_col_no = 'F'
row_no = 4

how do you form 'E4'?

That is closely related to point 1.
Were you able to implement point 1 first?
The "function call" mentioned in point 1 looks the same as "function signature" mentioned in point 2.

Have a look at this tutorial to see if it helps:
1.7. Print Function, Part I — Hands-on Python Tutorial for Python 3.1
1.11. Defining Functions of your Own — Hands-on Python Tutorial for Python 3.1

Or looking at it another way; in the following statement:

Code:

dpos = get_text_data(txt_filename)

(1) what is the name of the function? and
(2) what is the name of the parameter?

Now, if you remove the parameter, then what will the above statement look like? (Have a look at the tutorial; it tells you what a function parameter is.)