Preliminary processing and inspection of audio recordings are essential steps in environmental acoustics, bioacoustics, and acoustic monitoring of aquatic environments. This article aims to introduce the applications of the free and open-source software Audacity and to provide an educational guide for its use in visualizing, preliminarily processing, and organizing acoustic data from freshwater and marine environments. Using a tutorial and review-based approach, the article describes the principal stages of working with Audacity, from importing and quality-checking audio files to waveform visualization, spectrogram display, frequency-spectrum inspection, selection and labelling of acoustic events, basic signal processing, and preparation of data for subsequent analyses. Principles of metadata recording, file organization, and a proposed workflow for the systematic and reproducible use of the software in acoustic studies are also presented. Audacity can serve as an accessible and low-cost tool for teaching fundamental concepts of sound, qualitatively reviewing recordings, preliminarily identifying acoustic events, and preparing data, particularly for students and researchers. However, the software is not a substitute for specialized systems designed for calibrated acoustic measurement and advanced quantitative analysis, and such studies should therefore employ appropriate specialist methods and analytical tools when required. Overall, informed use of Audacity can provide a practical entry point for training and preliminary acoustic-data processing and can contribute to the development of aquatic bioacoustics and soundscape studies.