There's 100 levels of talents. You find the talentpage on the right side above "logout" button.
50 of those are gained by leveling (one point every 5 level, no cost to place it).

The remaining 50 are gained by "talent shards", which has a 15-30% dropchance depending on the difficulty of monster, only dropped by "Giga" version of said monster. Talent shard requires gold to spend, starting at 1000, and has a scaling with a total cost of roughly 13 million.

Talents you can get:
Critical hit (autoattacks - wands, bow/xbow, melee weapons) (max 15% chance, always 50% dmg increase)
Critical spellhit (spell+rune attacks) (max 15% chance, always 50% dmg increase)
Lifeleech (max 5%)
Manaleech (max 5%)
Both leeches has a diminishing returns if 3 or more monsters are attacked.

Currently the talent window doesn't show your current stats, you can write !talents in chat to see your current levels/values

Keep in mind, once you level a talent, you cannot revert it. Plan carefully when you place your talents.