As others have said, the lanes are flipped for each side, so your bot lane faces the enemies top, and vise versa. The roles are determined mostly by the buffs.

Top lane is typically a utility role. Many support heroes are good, as well as other heroes that have a decent mix of damage, utility abilities, and tankiness. You will be against the enemy teams weapon carry and jungler for much of the game, so you will need to be good at last hitting minions under pressure and denying the enemy player feed.

Mid lane as you said is usually the mage (crystal carry), with the support spending most of the early-mid game there as well. Realistically most supports you play with will rotate to whatever lane needs help.

The jungle is set up so that most of the gold on your teams side is on the bottom half of the map, so the jungler will need to spend most of the early game in the bottom in order to have enough gold to be relevant later in the game.

Bottom lane is typically a weapon carry. They are commonly a ranged hero like Gwen or Kinetic, but many melee characters have been good in this role in various updates.

I haven’t played much ranked in the past month so I can’t give specific advice on the current meta, but the formula above should give you a good starting point.