Verbs, not adjectives. A transitive verb requires an 'object' ie something the verb refers to : 'I gave her the hat' - 'the hat' is the object, the thing I gave to her. Sometimes the object is not stated explicitly : 'I gave it to her'. We know that 'it' refers to the hat.
There may be no apparent object, but it is understood: 'I gave' meaning 'I contributed' [to an appeal for support], 'I made a donation'.
Intransitive verbs do not require an object. 'I walked'; you can say where or how you walked, but these are not essential grammatically - you don't have to 'walk something'.
Sometimes English can be awkward : you can 'walk the dog' ie take the dog for a walk, but 'the dog' is not a grammatical object here - it's a description similar to 'walking the town' - walking around the town.