It is not really clear what you would hope to gain with what I think it is you are trying to do??
But to do what you ask:
alias hello='echo Hello'
Now when you type hello at the command prompt it will echo the word Hello, though not particularly useful in itself.
Normally aliases are used to help speed things up or perform a task with a single word, eg:
alias ll='ls -l'
alias df='df -h'
The first is to reduce the amount of typing but allow the original command to stay the same, namely ls.
The second you might perform if you decide you would always like to have the human readable form shown whenever you use the df command.