The first picture looks like you have a veritcal gap between the base of the object and where it starts printing the stringed section. 3D Printers work by depositing melted filament on something (like the baseplate, or a previous layer). They can’t start printing mid-air. If they do, they just leave strings of plastic behind. The second one doesn’t have any gaps, so it worked fine. I can’t really tell what the 3rd print is supposed to be, but it kinda looks like it should’ve worked.
Try enabling supports for the first object.
A temp tower can be downloaded from the 3D Print Guide Walkthrough, section 4. There’s also more objects and plenty of recommendations in the guide.