Software application architecture is the process of defining a structured solution that meets all of the technical and operational requirements, while optimizing common quality attributes such as performance, security, and manageability.
Start from here: Software Architecture and Design | Microsoft Docs
It would help you understand:
1. "What is Software Architecture?"
2. "Key Principles of Software Architecture"
3. "Architectural Patterns and Styles"
4. "A Technique for Architecture and Design"
Few tips: 10 Ways to Improve Your Software Architecture Design