things like leaves fall off (it cling into a branch) then fell. Fall down is used to things not attached to a particular part but fell like a ball.

It might help you to look at the little words - on and down - if you want to understand the difference between these phrases. 'Off' is the opposite of 'on'. So if the book is on the table, it can fall off. The leaves are on the trees, and then when autumn comes they fall off the trees. 'Down' is the opposite of 'up'. You build a house made out of cards (up..up..up) but then eventually this house will fall down. It's really quite simple if you think about what the words mean. These aren't phrasal verbs or idioms, they are just little words that mean what they on/off and up/down.

Fall Down is usually when referring to a thing or person who falls to the floor. Fall Off is when you've been 'on top of' or 'on' something. So you could fall 'off' a building or fall 'off' a wall. Be aware that 'fall out of' is also used. So if you're in a tree you 'fall out of' the tree.

Hello Not much difference. Both are intransitive verbs (this is a verb that is not an object/thing/person). I would use "It fell off" or "It fell down". Both are perfectly ok. If you were to trip up on your shoes laces onto the floor you would not fall off though you would fall down. I would use "Fall off" if lets say i were to fall off a wall. Hope i helped? English is hard, the grammar worse.