what is iupac name of (CH3)2CHCHO

 The brackets tell you that on that CH there are two methyl groups (CH3). Another way methyl groups could be written would be (Me)2CHCHO, although using "Me" for a methyl group is much less common. This is what the molecule looks like, if you're still not getting it: http://www.docbrown.info/page15/Image188…

Anyway, to name this what we need to do is find the longest carbon chain present in the molecule. Any way we slice it, the longest chain is 3 carbons, and there's a methyl group (CH3) on the second carbon in the chain. We also know the compound is an aldehyde based on the functional groups present.

Therefore, the compound is 2-methylpropanal

The "prop" part is like propane, because there are 3 carbons. You stick the "anal" part onto it because it's an aldehyde. The prefix of 2-methyl is because there's a methyl group on the #2 carbon.