how to change environment variable permanently

[Anil F Duggirala]

hello,
I would like to change the $PATH environment variable permanently, to
be able to execute a program more quickly.
I have tried adding a new line: export PATH=$PATH:/my/path , to my
.bashrc .
When I log in again, I see that $PATH is now: $PATH:/my/path/:/my/path,
my directory has been appended twice.
I don't know exactly what the "export" command actually does, so I am
lost here.
thanks for your help.