1 only will observation enable you to see exactly how something is done, but you'll be able to learn the technique of the person doing it. However, learning through observation may be harder than you think. This is because of learning.
2 An interview is a verbal interaction between two or more people where one (or occasionally more than one) person implicitly directs the flow of information (although this usage has been criticised by some particularly feminist researchers who dislike the implied inequality between interviewer and participant).