i am from Australia, searching for what engine oil to use on my cb500f, everywhere i go, it suggests either 10w30 or 10w40, i am unsure which one to use because supercheap auto is telling me not to use 10w30
Manufacturers rarely are in error when they recommend various lubricants for their bikes. 10-30 (Synthetic) is fine. In very hot weather, 10-40 is a good choice. I think the use of full synthetic oil should be mandatory, with a change interval for oil and filter at 3-4K miles, depending on your type of riding. Infrequent, short trips may require more frequent changes than longer trips and regular use. Your Honda has a rather large oil capacity for a relatively small (471cc) engine and more frequent changes generally should not be necessary.
My '27 CB-500F (bought new 4/'17) has just short of 10K miles and is about to have its 3d oil change.
I use 10/30 or 10/40 fully synthetic. I change oil and filter every 10,000 km (approx. 6,000 miles) and now have 180,000 km (115,000 miles) on it, and it uses no oil between changes and runs as sweetly as it did new. (2013 CB500FA)