You explained it very well.
Add this remark at the end of your achievement if you got all concepts of plagiarism.

please put a remarks,
"I have read and understood the Steemit Etiquette on Steemit Community and will do my best to embrace them" at the end of this task post.

Here on steemit for giving credit to the writer we use the source method. For as if you are copying some text from the internet or anywhere give its a reference.
for that, it easy just follow this syntax
[source](your link)

And the same way, if you are quoting someone line or some saying you can do with the help of this symbol ">". Place this symbol and paste the sentence. As you can see I have done the above. It will appear like this.

quoted sentence

For more details, you can read cryptokannon guide for achievement 3 from here Achievement 3 : Content Etiquette

Happy steeming )