While going through this section of the course, you have encountered built-in functions such as delay and Serial.println. These are just a few of the many built-in functions available in the Arduino platform. As well, we have only touched on some of the basic features in C++, and there are much more to the C++ programming language that we have not covered.
Even the most experienced programmer cannot remember all details of the Arduino built-in functions, so it's important for us to learn to refer to the Arduino documentations. Open the following link in a new tab, and refer to it often when programming.
For the C++ programming language, you can use the following tutorials to learn more
learn-c.org This is actually a tutorial for C, not C++, but nearly everything in C applies to C++ as well. It's a relatively easy to follow tutorial with an interactive tool that lets you test your code in the browser. Note that the printf statements in the tutorials needs to be replaced with Serial.print if you are using an Arduino.
Learn C++ This is a much longer tutorial for C++. The tutorial expects you to install compilers and IDE on you computer to try the examples, but you can also use a free online compiler like onlinegdb instead.