The key is to acquire small chunks of knowledge and then apply them in different ways. Input, process, output. Teach, solve problems, or build something. Retrieving information from memory is the process of learning. When you use information in a new setting, that’s when you start understanding it. 
One of the most effective approaches to acquiring knowledge is teaching. This is how Richard Feynman acquired knowledge. He selected a concept then taught it to an imaginary person. He spoke, wrote, and drew the concept to his ‘student’. When he got stuck or felt that an explanation was too wordy, he went back to the reference material. He continued this process until he could recall everything using simple explanations and analogies.