This chapter introduces ProtFlash, a novel lightweight protein language model that represents a significant advancement in the field of bioinformatics. By addressing the computational challenges inherent in protein sequence analysis, ProtFlash offers an efficient and accessible solution that combines innovative architectural design with practical applicability. The model incorporates several key technological breakthroughs, including a mixed-chunk attention mechanism that integrates both global and local attention patterns, and the implementation of RoPE position encoding for handling protein sequences of arbitrary lengths. This comprehensive guide details the model’s development, implementation, and practical applications in protein downstream tasks. It provides step-by-step instructions for utilizing the ProtFlash library ( https://github.com/ISYSLAB-HUST/ProtFlash ), including advanced techniques such as protein embedding generation and model fine-tuning using low-rank adaptation (LoRA) methodology. The chapter serves as both a theoretical foundation and practical handbook for researchers and practitioners in the field of protein sequence analysis and bioinformatics.