Power Query; help with left function

Hi last years I have use powerpivot.
Now I want to improve my skills and need some help.

Short version:
But my problem with query is,
I want to add some columns in my query.
I have use Left function but I cannot find out how I solve it in query


Long version:
I am working with accounting data from year 2018,2019 and 2020.
Until now I have added the data to one file.
Until now I have also made a small addition, I use left function for a few additional rows.

Now I want to use Power Query and combine my datafiles in some folder.
I can do that.

But my problem with query is,
I want to add some columns in my query.
I have use Left function but I cannot find out how I solve it in query

Why do I use left function?
I have accounting key which I want to split, I want to sort our by first number of the key, the first two etc.
The reason for that, if I group my accounting key, I get better informations.

In my file now I use: =left(accountingkey,1) etc


If accounting key is 1234, I want a coulmn with 1 and another with 12
If accounting key is 5432, I want a coulmn with 5 and another with 54
etc.

Thanks,

Possible Solution #1
Why not use the split function and split based upon length. Then merge columns as needed in new column and delete uneeded columns.

Possible Solution #2.
The correct syntax for =Left(Text,num_char) is
=Text.Start(text,num_chars)
In your case =Text.Start([ColumnName], 1) in one column and
=Text.Start([ColumnName],2) in the second column.