You create a .bash_profile in your home folder
Unless you are a .profile kind of guy.
The bash shell startup rules are to look for one of the following files in the following order and use the first one found as the shell initialization file:
.bash_profile
.bash_login
.profile
If non-exist, then nothing is used. When one is found, it is used, and the others (in the order shown) are ignored.
If you start a subshell from the current shell, then bash will run .bashrc, but .bashrc is not run on a new login (aka, when you start a Terminal session).
Many hard core terminal uses, split those shell initialization that persist, such as environment variables, and put them into .bash_profile. Those initializations that need to be done for each shell startup, especially if you create sub-shells, put those into .bashrc. Where those are things like aliases, shell functions, and various shell shopt and set -o options.
If what I just said is confusing, just put everything into a .bash_profile.
You will need to quit your Terminal session and start a new session so that a new bash is started, and the .bash_profile is read.