APA (7th ed.) Citation

Cutts, A., & Graser, A. (2018). Learn QGIS: Your Step-by-step Guide to the Fundamental of QGIS 3.4.

Chicago Style (17th ed.) Citation

Cutts, Andrew, and Anita Graser. Learn QGIS: Your Step-by-step Guide to the Fundamental of QGIS 3.4. 2018.

MLA (9th ed.) Citation

Cutts, Andrew, and Anita Graser. Learn QGIS: Your Step-by-step Guide to the Fundamental of QGIS 3.4. 2018.

Warning: These citations may not always be 100% accurate.