Bot lane is highly critical because you are the damage dealer. Bot laners will often opt for ranged, sustained damage dealing champions. although frail, they are the ones then 9 times out of 10 decide the game during team fights. It involve a lot of skill.

During the first 30 second of the game, you will be waiting for minions and monsters to spawn. The pictures shown are where a bot laner would usually wait for minions and get vision on the enemy.

CS means combat score, and you gain cs by killing minions or monsters. CS only counts by killing, not damaging, because an ally minion or champion can steal the kill. CS will grant you gold. You can think of CS as last-hitting a minion for the gold. Otherwise it will be wasted and no one, or someone else, gets the gold. You want that gold because it stacks up. Only difference is Support is cs-ing with you.