You can maintain 3 types of family trees that you can have on your Family Site:
1. An Online Tree:
This tree is started directly on your family site. It can be edited and viewed online, in your Family Site. You can choose to let your Site Members edit the tree as well. The information in this tree can be backed up on your computer by exporting a GEDCOM file in the Family Tree > Manage Trees page.
2. A GEDCOM Tree:
This is basically an online tree, which was not started from scratch. It was either imported from Family Tree Builder, or another genealogy software or website. You can import any standard GEDCOM file to your Family Site, in the Family Tree > Import GEDCOM page. Once imported to the site, it can be edited as an online tree. You can download the original GEDCOM that you uploaded at any time, by using the Download option in the Family Tree > Manage Trees page.
3. A Family Tree Builder tree:
This tree is built using our Software – Family Tree Builder (FTB). FTB needs to be installed on your computer (http://www.myheritage.com/family-tree-builder) and you can start building the tree.
The tree is published from FTB to the Family Site, where it can be viewed, but not edited (the next version of FTB will allow online editing of FTB trees). If your computer is damaged, you can always recover the tree from the published version on your Family Site, with the photos.
It is also possible to have an editable copy of your tree online: If I use Family Tree Builder can I still have a tree I can edit online?