1. To learn or become knowledgeable about every or nearly every aspect of something, from the most mundane to the most nuanced. After working at this company for nearly 30 years, I've learned it from the bottom up. As the chief tax law specialist, it's my role to learn these new tax regulations from the bottom up.

2. To become knowledgeable about or skilled in something by beginning at the most basic level and then working one's way up to the more complicated or difficult aspects. I actually never had any sort of preternatural skill with mathematics—I had to learn it from the bottom up, just like most other students. I hard forgotten everything I knew about Japanese, so when I started studying it again in my 30s, I had to learn it from the bottom up all over again.