You can find a bunch of tutorials on YouTube about how to get started, but I say, start with (Ctrl + space)

IEC 61131–3 has an amazing GUI especially for those wanting to learn Structured Text (ST). Create a program (PRG) for example, and hit [Ctrl + space] in the body, and the GUI will tell you most, if not all of the valid instantiations, reserved words, and data types at the time hitting this hot key combination.