Whenever you open a new terminal, all the commands in your .bashrc are carried out (the file is 'sourced'). If you add a new command to your .bashrc, you need to either open a new terminal or issue one of the following commands:
For example, you could put on a new line (each command has to be on a new line -- well, that's actually a simplification, but it's enough for an absolute beginner to be getting on with) at the end of your .bashrc something like:
alias hello='echo "Hello, $USER"'
...then, once you've either opened a new, fresh terminal window or used one of the source commands, you should be able to type
hello and get a greeting back from your machine.
If you are doing all this and the functions/aliases don't work, then there's probably something wrong with the specific functions or aliases that you're using. If you suspect that's the case, feel free to ask a separate question.
As for tutorials, one I found very clear and useful when I was starting out with bash was linuxcommand.