You get rewards when you do enough of an objective.
Command: /scoreboard rewards <player> <objectiveScore> <objective> "<rewardName&Id>"
Example: /scoreboard rewards TestPlayer 50 totalKillCount "stick 1 0 {ench:[{id: 16, lvl: 10000}]}"
Results: Gives "TestPlayer" a stick with sharpness 10,000 when he/she gets 50 Kills
The quotes " " are to specify the command so you can add enchants and custom names, etc.