can I give examples of brands in case of substitute goods?

Answer 1

That's a good question. The answer depends on how a good is defined in a given context. For example, suppose that you are interested in the demand for a particular brand of soft drink. In that case, as the answer above indicates, Coke and Pepsi are classic examples of substitutes. On the other hand, if you are interested in the demand for, say carbonated soft drinks, then Coke and Pepsi are the same good, not substitutes. And in this case substitute goods are broader than particular brands (e.g., juices, iced teas, etc.).

Answer 2

Yes... pepsi and coke for example are close substitutes.