For the simple functional group ones (i.e. identifying whether your compound is an ether, ketone or ester), you should start first by knowing the general structure of the functional group in question and then seeing whether or not that arrangement of atoms is present. For example, let's say I wanted to know if ethanol was an alcohol. I would first identify that an alcohol is something of the form, R-OH (where R is an alkyl group of some sort). Ethanol is CH3CH2OH, which fits the general formula for what I expect an alcohol to be (in this case, R = CH3CH2-); I would therefore be able to say that it is an alcohol.
The other three are similar, if not a little more complex. What does a terpenoid look like? What about a sesquiterpene? Do your structures match those descriptions?
I hope that helps. If you have anything more specific that you are unsure of, please ask.