A Portfolio is simply a way of logically organising/grouping Plans.
To create a portfolio, go to the Portfolios tab and select the Add Portfolio icon from the Tool ribbon.
When you are added as a licensed user of PM3 a ‘special’ Portfolio is automatically created called ‘Your name’s Root Portfolio’. You can then add a hierarchy of Portfolios under this Root Portfolio in order to logically organise the Plans that you add via Add Plan. This is very similar to organising MS Office documents within folders.
NB: Organizational Portfolios can only be added by an Administrator.