I have an urgent question.

I'm going to Australia for my holiday. I can speak English pretty well and i could practise it while I was there.
(is it grammatically correct? Is the meaning that of a conditional clause?

Thank you very much in advance

Your English seems nearly perfect - but you should always capitalize the pronoun 'I' when using it - and brackets should be used before the full stop. Otherwise, your English seems fantastic.

There is no conditional clause in here:

I'm going to Australia for my holiday. I can speak English pretty well and i could practise it while I was there.

Check out the explanations and examples here, and then repost when you're ready.
http://www.ego4u.com/en/cram-up/grammar/conditional-sentences

Yes, your sentence is grammatically correct. It is indeed a conditional clause. You are stating that if you go to Australia for your holiday, you will have the opportunity to practice your English while you are there. The verb "could" in this context is used to indicate possibility or potential.