You should provide more information about what you are expecting to see and what you are seeing instead to get a more precise answer.
I am guessing that recent updates to the XLSX package may use a different syntax than the older version used in the tutorial.
The code below will read your Excel table into a DataFrame and then access the first column.
using DataFrames, XLSX
G = DataFrame(XLSX.readtable("data/zillow_data_download_april2020.xlsx", "Sale_counts_city"))
first_column = G[:, 1]
Resources:
https://felipenoris.github.io/XLSX.jl/dev/tutorial/#Read-Tabular-Data
https://dataframes.juliadata.org/stable/man/working_with_dataframes/#Working-with-Data-Frames
https://tables.juliadata.org/dev/#Using-the-Interface-(i.e.-consuming-Tables.jl-compatible-sources)