The "Current" values listed are the start and end dates of the projects at this exact moment. The "Initial" values, however, are the start and end date associated with the project when it was first created.
As an example, say I create a project and expect that project to start on 2/15/2016 and end on 5/15/2016. I would then use those dates and the start and end date for the project when I initially create it. Those dates then become the projects initial start and end dates. If, a few days later, I realize those dates are not correct and need to update them, the new values become the projects "Current" start and end date, while the project's "Initial" start and end date are still 2/15/2016 and end on 5/15/2016.
The project's baseline is added to a project by accessing the project's detail page, clicking "Actions", and then selecting the "Add Baseline" option. This can only be done on projects you manage.
I hope this has added some clarity to the different types of project dates. If you have any additional questions or concerns, please let us know.