This is the 68th most frequent Hungarian word.
fontos
Important.
In this sentence, 'fontos' is an adjective used to qualify the noun 'döntés' (decision) as being significant or of high importance.
Ez egy nagyon fontos döntés.
This is a very important decision.
Here, 'fontos' is part of a subordinate clause, expressing an abstract necessity or importance related to the subsequent action.
Fontos, hogy mindig őszinte legyél.
It's important that you are always honest.
In this instance, 'fontos' serves as the main descriptive trait of 'bizalom' (trust), signifying its essential role.