Lanes are the main paths that creeps follow in the course of a game. Lanes are defended by towers, and in order to push the enemy into their base and destroy their barracks and Artifact, each successive tower in a lane must be destroyed before damage can be dealt to the next structure. Along each lane are located areas of fog of war for tactical maneuvering, such as juking and ganking. Controlling a lane is a key tactical component of gameplay; early lane control in a game can put your opponents at a disadvantage by keeping them away from your towers and denying last hits on creeps for much-needed minerals.
Right now, the general rule is that one champion goes long lane, one goes to the jungle, two go short lane, and one goes in the middle. If you are having trouble with the hero(es) you are facing, you should ask someone to switch with you.