Unable to link Terminal to macport

[Mine]

Hi,

The first time I installed macports OSX 10.4.11,  II was able to
download and install applications. Now that I have relaunched
Terminal a few days later, I don't know have to relink the Terminal
to macports. if  I type sudo port selfupdate, I get the following error:

sudo: port: command not found

The documentation mentions a ~/.profile. Is this a file I can open
and edit, because I can't find it.

Can someone please tell me how to get the Terminal to reuse
macports. Simple info would be nice as I new to Terminal,
and this way of working.

Thanks,

Terrence