What is a methodology ??

A set of principles, practices, procedures, and rules that teams and organizations use to guide their work throughout the project lifecycle. The method provides a structured approach to planning, executing, and controlling information systems development or project management processes.

WaterFull methodology :

The term "waterfall" implies a one-way progression, suggesting that once a process is initiated, there is no room for alterations or revisions upon completion. For example, in the context of developing a web application to manage equipment, when the client provides specifications, any adjustments or modifications become impractical once the project is underway. In this methodology, flexibility is limited, as the work adheres to the initial specifications from start to finish.

Agile methodology:

In the Agile methodology, the project is divided into multiple iterations, with each iteration encompassing various phases. Typically lasting between 2 to 8 weeks, each iteration follows a cycle where software is developed, released, and refined based on user or customer feedback.
The Agile model operates by initially delivering a version of the software in the first iteration. Subsequently, feedback is gathered from end users or customers regarding the application's functionality and features. This feedback is then used to make improvements and incorporate necessary changes into the second iteration. The refined software is released once again into the market during the second iteration. This iterative process is repeated in subsequent cycles, allowing for continuous improvement and adaptation to evolving requirements or preferences.

In which scenarios should I choose the Waterfall model, and when is it more appropriate to opt for Agile?

The choice between the Waterfall and Agile models depends on the nature of the project. If the project has a specific goal from the outset, and the client provides a detailed specification that is unlikely to change, the Waterfall model is suitable. However, if there is an expectation of future modifications based on client feedback, the Agile model, with its flexibility, becomes the preferred approach.