If you say you are seeing someone there could be uncertainty about how you feel about the person -- you are still getting to know them.
If you say you are dating, you definitely like the person but haven't decided on the sustainability of the relationship.
usually it means that they're someone new that I'm physically or romantically interested in but have not got to the point of getting into a relationship with them.
Some persons do not like to put a label on the relationship too quickly, so they say nothing until the feelings are understood.
Beyond the label, I'm not sure how to define what it is.
Plentyoffish dating forums are a place to meet singles and get dating advice or share dating experiences etc.
Hopefully you will all have fun meeting singles and try out this online dating thing...