The title or position of webmaster is like that of system administrator - most people don't go to school or plan to become either but find themselves in the position of doing the job. Whether you were the "go to" computer person at work and were nominated without your input or you have decided to run your own website blog or ecommerce you are going to find that there is a lot to learn. Some suggestions for those just starting out:
Don't try to learn everything. There is a lot of technology out there and it is easy to get caught up in all latest protocals, languages, methods and techniques. Pick an area of technology you want to learn and go for it. Add to your toolset and visit other technologies as you feel comfortable. This recommendations comes from my observation of other people and myself. Getting caught up in perl, php, python, C, java, linux, windows, joomla, drupal and on and on can be a full time job on its own. Getting too caught up in the technology can make you idle. Use this site and others to get an idea what meets your requirements and start testing it out.