'How to group by month with days

I'm new to SQL and I could use the help. I have a data set which I need to filter down. The data looks like this:

code is nvarchar(85)
date is nvarchar(10)
quantity is numeric(38,15)

I'm tasked to get a list of data for the one code (code1). This data needs to show the quantity grouped by date. In months.

What's best way to do this with a bit of explanation behind it?

sql

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