Learning how to work in automation is very much like learning a new language. ISA's web site has all the information you need to read, write and compose in this new language.
Process engineers, using the process flow diagrams and symbols created by ISA, design plants. You can find these symbols, the standards for using them, and tutorials and training on how to read and use them on the ISA web site.
Automation engineers take the process flow designs and turn them into automation system designs. They produce piping and instrument diagrams (P&IDs), they use the instrumentation and measurement symbols that ISA created to label instrument loop diagrams, and they use function block diagrams to design and program the control systems to operate the process engineers' design. ISA has standards on documentation of control system design so that you can learn to update your as-built drawings correctly. This makes upgrades easier, maintenance more reliable, and reduces the chance for accident and safety incidents.
The ISA web site has all the information on symbols and terminology, from the standards that created them to the tutorials on using them that will help you learn this complicated language so you can become an automation professional.