cp copies a file. The first argument is the file to copy, the source. The last argument is where the copy goes, the destination. The source stays where it is.

Copy to a new name

Make a copy before you change a file. If something goes wrong, you still have the original:

learner@tidepool:~/shop$ cp prices.txt prices.bak
learner@tidepool:~/shop$ ls
prices.bak  prices.txt

The two files have the same text.

Copy into a directory

When the destination is a directory that exists, the copy goes into it and keeps its name:

learner@tidepool:~/shop$ cp prices.txt backup
learner@tidepool:~/shop$ ls backup
prices.txt

Give more than one source to copy them all into the directory. The directory is always the last argument:

learner@tidepool:~/shop$ cp monday.txt tuesday.txt backup

cp writes over files with no question

If the destination file exists, cp replaces its text with the text of the source. It does not ask, and it does not warn you.