When you add a suffix to a word ending in 'fer' you sometimes need to double the 'r', but how do you know when? When you add a suffixes and the second syllable of the new word is stressed, then you ...

I’ve told you, fur doesn’t tan, even when you’re in the garden. A suffix is a letter or group of letters that go on the end of a word. They change a words meaning. ‘Ing’ can change a noun into a verb.