Deduplicating a list
Removing repeated lines is the sort of thing a spreadsheet can do but rarely without a fight. Paste the list here and it happens as you type, with the original ordering preserved — the first occurrence of each line stays where it was.
The three options exist because “duplicate” is not one definition. Two lines that differ only in capitalisation are duplicates in a list of email addresses but not in a list of API keys. Two lines that differ only in trailing whitespace are almost always duplicates, but the whitespace is invisible so the problem is hard to spot. Turn on whichever rules match your data.
Next steps
To put the deduplicated list in order, use sort lines alphabetically. To see what changed between two versions of a list, the text compare tool shows a line-by-line diff.