Okay, so best beginning champions for each role
Top:
Garen (Flash/Teleport)
Kayle (Flash/Teleport or Flash/Ignite)
Riven (Flash/Ignite or Flash/Teleport)
Malphite (Flash/Teleport)
Jungle: (Experienced)
Amumu (Flash/Smite)
Shyvana (Flash/Smite)
Vi (Flash/Smite)
Middle:
Annie (Flash/Ignite or Flash/Teleport)
Veigar (Flash/Teleport)
Twisted Fate (Flash/Ignite or Flash/Teleport)
Syndra (Flash/Ignite or Flash/Teleport)
Lux (Flash/Ignite or Flash/Teleport)
Bot: Attack damage Carry & Support
ADC: only take Flash/Exhaust if your support is taking Heal
Ashe (Flash/Heal or Flash/Exhaust)
Miss Fortune (Flash/Heal or Flash/Exhaust)
Sivir (Flash/Heal or Flash/Exhaust)
Jinx (Flash/Heal or Flash/Exhaust)
Support: Usually always take Flash/Exhaust unless you know the power of your champion can use ignite to win a lane
Blitzcrank (Flash/Heal, Flash/Exhaust, Flash/Ignite)
Annie (Flash/Exhaust or Flash/Ignite)
Morgana (Flash/Exhaust or Flash/Ignite)
Janna (Flash/Exhaust or Flash/Heal)
Leona (Flash/Exhaust or Flash/Ignite)
My Advice for beginners is jump into a custom match as soon as possible and don't put any bots in, go into a lane by yourself and learn how to last hit minions, its crucial, unlike other moba games, you have to be the one to finish off the minion in order to be credited gold for the kills, if you miss you wont get the gold of killing it but you will still be in EXP range.
Another thing is to probably play with another player to get the ropes down so when you're inevitably going to be flamed by other players you have someone who has your back and can keep the good~ish mood rolling.
Lastly, find a champion that you feel like calls to you and just keep playing them, its really fun to just fall in love w/ a champion and main them until you're rewarded for your hard work, but in the beginning it will be slow since you have to learn over 140 champions and their 4-12 abilities, and how they work, not to mention Damage scaling and how to build your champion through the shop and what items are good when.
If you want someone to play with I'm more commonly on League than I am on Xbox, due to family. Just send me a Friend request & we could hop into the discord to play sometime & I can throw my knowledge at ya.
My Summoner name to add: BossPirnie
My OP.GG if you wanna take a look @ my best champions and what not:
http://na.op.gg/summoner/userName=bosspirnie