Custom PC building involves assembling a personal computer tailored to specific needs and preferences. This process allows users to select individual components, such as the CPU, GPU, motherboard, and RAM, ensuring optimal performance for tasks like gaming, graphic design, or general use. By choosing parts that fit their budget and requirements, builders can create a machine that meets their exact specifications. Additionally, custom PCs often offer better value and upgrade potential compared to pre-built systems, making them a popular choice among tech enthusiasts and gamers alike.