You can spend your skill points at any time and it doesn't cost you anything. This leaves you with 58 skill points to spend on a max level character with fully unlocked Renown. You can also unlock 10 additional skill points through the Renown system. You get one skill point each time you level up, starting from level 2. These passives are a lot stronger than all the others, but similar to Ultimate skills you can only pick one.

33 points: The final cluster only has several Key Passives.Unlike other clusters you can only have one Ultimate. Ultimate skills are extremely powerful skills with very long (45s+) cooldowns. Here you get your Ultimate skill with its upgrades and more passives. Usually some defensive and mobility skills, but also some more damage-oriented skills, which are more complex and conditional than Basic and Core skills. The next 3 clusters contain a variety of skills and passives. 6 points, 11 points, and 16 points: Unique clusters per class.Core skills are generally your main damage dealing skills they deal substantially more damage than Basic skills at the cost of your resource. Contains Core skills, their upgrades, and some passives. Many of them help you generate your Primary Resource. These skills are your weakest attacks but they have no cost or cooldown. Here you have only your Basic skills and their upgrades. It doesn't matter where you put your points, you just need to hit a certain number of points invested in total. Each cluster is unlocked as you put more points into the skill tree. The Skill tree is divided into 7 clusters.

Diablo 4 skill tree calculator