Performance bonuses are fairly strictly-defined. They're automatically counted as "earned" for cap space consideration, but don't have to be paid unless earned. There are two categories of bonuses which can be paid:
1: Individual "A" Bonuses - These are broken into categories like ice time, goals, and plus/minus. Each category has a minimum requirement a team can bonus for (10 goals, for example) and each category may not create more than $215,00 worth of bonuses (you can bonus $100K at 10 goals and then $115K at 15 goals if you want). Total "A" Bonuses can't exceed $850,000.
2: Individual "B" Bonuses - This is kind of a two-part bonus system based on performance comparative to the rest of the league. First off, the league itself will pay the player a bonus outside of his Club-paid salary if he does things like earns a place in the top five for postseason awards like the Hart, Selke, or Vezina; or if he places top ten in the league in offensive/goaltending categories. On top of the league bonuses, the club can pay bonuses of up to $2M to the player for making these awards.
Basically, entry-level deals are a great way to inflate a cap hit without inflating a salary number. You have to offer the league minimum ($525,000 this season), but can't pay a player more than $925,000 in regular salary plus $850,000 in A bonuses plus $2,000,000 in B bonuses. This is how you get the maximum $3,775,000 hit for guys like Justin Schultz, who is a great example of a drafted player waiting until he's old enough to reach free agency.