Learn System Design Fundamentals and Build Systems At Scale

System Design is the systematic approach that covers a wide range of engineering concepts and principles for designing scalable systems that are modular, reusable, and extensible.
Low-Level Design is the process of designing software components, interfaces, and modules of systems in a modular, reusable, extensible manner to meet the current/ future needs of any organization. High-Level Design digs into depth of all related variables, including architecture, required hardware/software components, how data travels and is stored throughout the system, and how caching is done to optimize the system for fast response times and reduced costs, etc. This includes choosing what kind of database to use, like Cassandra or MySQL or something else, and making choices like SQL vs. NoSQL.

A software engineer who understands both High Level and Low Level Design performs better. It enables an engineer to make architectural decisions to make the software system efficient and scalable while saving an organization's cost. It allows one to distinguish between available databases, e.g., MySQL, PostgreSQL, etc. It also enables one to find the best tool to solve a particular engineering challenge, with tools like Messaging Queues, Load Balancers, etc.
System Design will:

Enhance the quality of software systems developed by engineers

Save long-term engineers costs for a company

Make software systems able to handle changing product requirements and also handle large scale

To become a jack of systems design, you need to take into account the following when building a software system:

Understand the product requirements (current as well as future) and edge cases very well

Create and document software and System Design, which includes Class Diagrams, Schema Diagrams, Architectural High-Level Diagrams

Understand the pros and cons of every software system like Databases, Caches, etc., and when to use them