Support, ADC, APC, Assassin, Bruiser, Off-tank, Tank Differences
Start with their kits, and go into detail later in this section to start though
Support-Leona, Soraka, Thresh, Sona-A support is a champion that kit is built around being a support, most supports aren't classified as only support in fact, no supports are solely supports. A support champion needs to have a kit that help their adc, and later their team, stuns, silences, snares, knockups/backs, steroids, heals, shields just to name some, and they scale very well with supportive items like Ardent Censor and usually grab a gold related item for them to get gold throughout the game without starving the adc of their gold.
ADC-Ashe, Miss Fortune, Corki, Vayne-A marksman champion that relies solely on their auto attacks and very little on their actual abilities, these champions rely the most on items to ditch out their damage unlike any champion in this game getting the right items for the right circumstances is essential, building very little defensively but instead looking to completely devastate the entire enemy team.
APC-Annie, Morgana, Lissandra, Syndra-A mage, these champions rely heavily on their abilities to ditch out their damage and should never be taking lightly or underestimated, they as well don't really depend too heavily on defensive items, but their items are designed to increased how much damage their specific abilities do. They are the early game and early mid carries and usually they start losing damage output late game.
This next section gets a little more confusing because the next 4 roles depends solely on what items they grab throughout the game.
Assassins-Assassins are designed to not really ditch a whole lot of damage to the enemy team but specialize in taking out priority targets like Mages and Marksman. They are usually very mobile and hard to pin down and usually have some way to initiate and to get out and kill their opponent before the enemy team has a chance to react. Assassins unlike any other classification build absolutely no defensive items, they need to go full on assassination to be effective. Some assassins like Master Yi, Jax, Tryandamere, Vi, are some examples of assassins, though they are also fighters which means with a few changes in their builds they could be bruisers.
Bruisers-Bruisers again most of these fighters are also assassins like the names mention above while others are more tanky in their design this classification is the most situational type classification as they can build up to 3 defensive items to only 1 and still be very effective due to their unique kits like Jarvan IV, or Gangplank, some assassins like Rengar, or Pantheon could also fit in this category depending heavily on how they build their champion.
Off-Tanks-Most confusing type of champion nobody seems to know what a true off-tank is off-tank build at most 2 offensive items, and at the very least have 1 they are not pure tanks but could just as easily fill the full tank role if instead they elected to build full tank, like Warwick, Trundle, Udyr, Shen.
Tanks-Tanks build solely defensively usually having kits designed to taking a beating, tanks could range from supports, bruisers, to off-tanks depending on how they build there champion. Arguments over what these champions should build come up all the time and is a huge debate even with my cousin and I as he believes that a tank should grab at least one offensive item, while I believe that to be a true tank u should build full tank as your kit does the damage that is necessary for you to be effective, some examples, last game I played this Poppy that grabbed Maw of Malmortius and Trinity Force though very useful on her grabbing these items made her more of an off-tank rather than a true tank. Some better items for tanks could be spirit visage instead of Maw of Malmortius, or to do a little more damage Titantic Hydra would of been nice, or even Black Cleaver, Frozen Mallet as all these items are tank items just the same.