Comment on MacPorts

Just a quickie question (I'm sorry for asking in here, but...) :

Most of the time when I install commands with this (or when I build them manually), they never seem to 'kick in', as they don't seem to be in my PATH. Now, I know this is super basic stuff, and there are numerous info places on the web, but I'm still confused; exactly which profile file am I supposed to edit on my system (OSX 10.4.10 using bash), and it would be great to see an actual example on how it could look like in that file. (I realize I should ask this somewhere else, but I'm so desperate to get this PATH enigma over with.)