Message in terinal box re updating my account to use zsh?

There are several command shells around on macOS, as sagely mentioned in the reply above. bash is one, and will remain around, but it’s not getting updated. Apple has decided that newly-created Mac logins will get zsh, not bash, and not (IIRC) tcsh that was the default shell for Really Old Mac logins.

You can switch to zsh (or to another shell, or even install yet another shell and switch to that), or can do nothing and ignore that message, or can set up a shell symbol to suppress that message*, your choice.

Here is the linked article: Use zsh as the default shell on your Mac - Apple Support

*to suppress that message (see the linked article):

export BASH_SILENCE_DEPRECATION_WARNING=1

If you use the Terminal infrequently, or are content using the circa 2007 Bash shell, then you need do nothing. If you want an Apple supported Shell (Zsh), and willing to learn its strengths and differences from the Bash Shell, then run that command as shown in your Terminal message.

The Zsh shell does not read the Bash dot files, and uses a different Terminal (PS1) prompt syntax.

Only if you choose to switch to the Zsh shell as the default, copy and paste the following into the Terminal and then press return. This will set your default PATH and PS1 Terminal prompts for Zsh, and the .zshrc dot file that the Terminal reads when you launch it.

<<"EOF" > ~/.zshrc
export PATH=".:/usr/local/bin:${PATH}"
PS1="%m: %~ %% "
EOF

Again, only if you switched to the Zsh shell, run this after the preceding HERE script is done:

source ~/.zshrc