The verb stem is bit-boon or in IPA: [ˈbɪtbun]
You should by now be familiar with the pronunciation of the pronoun prefix and glottal stop ngah- [ŋaʔ].

nga-h-bidu-n
I-happening now-climb.up-non.past tense.

-bidbun belongs to the class of verbs that end in -bun. There are many other pronoun prefixes that verbs can take. We have been using nga-h- meaning 'I [now]' for the verbs we have been learning because verb stems have to take a pronoun prefix of some kind. Remember the glottal stop represented by the 'h' means 'happening right now'. Here are some others prefixes for both Kunwinjku and Gundjeihmi. If you're learning Kuninjku or Kune, then it's the same as for Kunwinjku.

ngarr-bidbun (W) arr-bidbun (Gdj)
kane-bidbun (W) gani-bidbun (Gdj)
ngane-bidbun (W) ani-bidbun (Gdj)
ngarri-bidbun (W) arri-bidbun (Gdj)
karri-bidbun (W) garri-bidbun (Gdj)
yi-bidbun (W/Gdj)
ngune-bidbun (W) nguni-bidbun (Gdj)
ngurri-bidbun (W) wurri-bidbun (Gdj)
ka-bidbun (W) ga-bidbun (Gdj)
bidbom (W) ba-bidbom (Gdj)
kabene-bidbun (W) gabani-bidbun (Gdj)
bene-bidbom (W) bani-bidbom (Gdj)
kabirri-bidbun (W) gabarri-bidbun (Gdj)
birri-bidbom (W) barri-bidbom (Gdj)

If you want to brush up on the meanings of these pronoun prefixes, go back to the blog post here:
http://bininjgunwok.org.au/2012/07/

present and future -bidbun
past completed tense -bidbom
past continuous tense -bidbuni
negative, should have (irrealis) -bidbuyi
command -bidbu

Kunwinjku example:
Ku-wohngorrk yi-bidbun ka-yo kun-rodjbe. (W)
Climbing half way up [the scree slope] there is red ochre there.

Gundjeihmi example:
Wanjh njamed Yigarrradadjgi arri-djoukgeyi, ngarri-yoi yigakbe, malaiwi wanjh Balawurru ngarri-bidbuni. (Gdj)
Well, we'd cross over at whatsit, at Yigarradadjgi, and sleep there for one night, then the next day we'd climb up at Balawurru.

Yi-bidbu! (W or Gdj)
Get in (the car)!

Kalawan ka-bidbun ku-rrulk. (W)
Galawan ga-bidbun gu-rrulk. (Gdj)
Goannas climb up trees.