"Certainly" is an adverb used to express agreement or affirmation. It indicates that something is true or that a response is positive. For example, if someone asks, "Can you help me?" responding with "Certainly" conveys a willingness to assist without hesitation. In conversation, "certainly" can also serve to emphasize confidence in a statement. It reassures the listener that the speaker is sure about the information being shared. This word is commonly used in both formal and informal contexts, making it a versatile addition to everyday language.