A first step might be to add family that you know about, parents, siblings etc. Don't worry about getting everything correct and accurate at first, most things you can enter allow you to mark them as uncertain, later when you get evidence your can improve and correct.
Do not forget to add the sources of your information, in the beinging it will be mostly personal memories which is ok to start, later you will be collecting official documents to back up your work.
The main thing is to enjoy unravelling your story.
As your tree grows you can search for matches and people with the same family names, it gets addictive.
