If you have friends to instruct you in how to play and build certain characters taht would be the best advice. Playing easy champions would be something you should look up to while trying to udnerstand the game. The game isalways being updated so whats good now might not be good tomorrow or in a few weeks or months so grasping as much knowledge about champions is never bad, but wanting to learn all champions will make you fail at mastering them, so focus a few champions per lane at start, i can give you a few easy champions to get into. Top: Garen, easy all around, good duelist and good damage output, skills have decent cc and don't cost mana, perfect for starters since your only concern is to farm and being able to outdamage your enemy. Mid: A safe pick would probably be Veigar, almost no skill required, most of your skills are point and click and you get free ap for farming with your skills, you can farm safe and get strong without having to battle it out with the enemy for gold. Bot: A safe pick would be Tristana, good duel potential, can go in and go out of fights and her kit makes her one of the dedliest carries since she has a lot of mobility and attack speed, combined with some burst. Support: A good support to start would be something like Sona, she has some decent healing and buffs to your ADC and you can just sit back and let your ADC work, but you can also go in and harass the enemy if you feel confident, up to you. Jungle: good jungler to start would be something like warwick, self healing with decent clears and gank potential
Hope i helped you and gl, you can also watch some guides on youtube to help you out with certain roles and champions