Learning new tools, programming languages, algorithms, middle-ware, or even math is a way of life for any roboticist. And learning fast is equally important. Here are some useful platforms for learning.
Assuming you already know how to code, learning a new language involves getting familiar with new syntax, libraries and sometimes new paradigms. Interactive learning is great because you start writing code from the very beginning. HackerRank and Codecademy are really useful for this.
Learning within community is both helpful and fun. The nice thing about online communities is that they transcend geographic location, age and level of expertise. Communities I like are Stack Overflow (ask developer questions), ROS Answers (ask robotics or ROS questions), GitHub (share code) and Quora (share knowledge).