Introduction
Definition of Software Engineering:
Definition by Standard Glossary of Software Engineering Terminology
"The application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software."
Textbook
If you like reading a book, I recommend "Head First Object-Oriented Analysis and Design by Brett D. McLaughlin, Gary Pollice, Dave West".
This book covers object-oriented design principles and practice. It is 600 of the easiest textbook pages you will ever read; the concepts are not deep and the book hits every point from many angles.
info
Whether or not reading the optional textbook, you must follow the readings posted on the website.