The add -ed to make the past simple and past particple. If the word ends with -e, then just -d is added. If the word ends -consonant + y, the the 'y' is removed and -ied is added. If the verb has one syllable and end -1 vowel + 1consonant, then the final conconant is doubled. In bE we also doublt the final 'l' in verbs like 'travel'.