1.) To form the past tense of verbs ending in -y, you usually change -y to i and then add -ed or -d. If a vowel comes before the letter y, change -y to i and then add -d only. If a consonant comes before the letter y, change -y to i and then add -ed.

lay-laid, pay-paid, say-said, carry-carried, hurry-hurried, cry-cried, fry-fried, fancy-fancied, marry-married, bury-buried, tally-tallied, deny-denied, try-tried, supply-supplied

2.) There are exceptions to the first rule, of course. Some verbs ending in y form the past tense by adding -ed only.

pray-prayed, stray-strayed, stay-stayed, delay-delayed, relay-relayed, destroy-destroyed, prey-preyed, toy-toyed, deploy-deployed, play-played, replay-replayed

3.) To form the past tense of some verbs, you need to double the final consonant before adding -ed. This is to keep the vowel sound short and to avoid changing it into a long vowel sound which can change the meaning of the word.

hop-hopped (not hoped), star-starred (not stared), rapped (not raped), bar-barred (not bared), tap-tapped (not taped), can-canned (not caned), plan-planned (not planed), pin-pinned (not pined), clap-clapped, jog-jogged, sag-sagged, enrol-enrolled (though “enroled” is also used), wrap-wrapped, skip-skipped, dip-dipped, flip-flipped, trip-tripped, lag-lagged, beg-begged, flop-flopped, trap-trapped, hug-hugged, plot-plotted, rot-rotted, spot-spotted, strut-strutted, plan, fan-fanned, sin-sinned