Digital camera lenses

I need some info on thread sizes for zoom lenses like the tamron, 28-300. I have a camera with a 58 mm thread and I would like to know what is the best choice for an accessory lense?
What does it mean that a lense fits the Canon AF, etc..?
I would appreciate some help, please.

The thread size of 58mm refers to the filter size which attaches to the front of the lens.

When it says "fits the Canon AF" it means that the lens is designed to fit a Canon auto focus camera body that accepts interchangeable lenses. Each camera body (SLR) has a specific mount that the lenses must mate in order to work. i.e. Canon EOS lenses for EOS cameras, Nikon mounts for Nikon cameras, Minolta mount for Minolta cameras, etc.

why not make all lenses fit all cameras..? dam.
can you buy a conversion mount that mounts canon lenses on nikon bodys?

Same reason Ford parts don't fit Chevrolet.

I have a Sony F717 cibershot camera with a carl zeiss lense that is preety good but I would like to add zoom lense to it. Do I have to stick with Sony?

That's a fixed lens. You cannot change the lens. You can add accessory lenses/filters to the front of the lens. Those accessories need to have 58mm threads. See your manual or the Sony site for specific accessories that are available.

I suspected that. You have been very helpful. Since you really know about this, I would like to ask another question if you don't mind.
What does a 2.0 telephoto converter is capable off?
What about a 0.7x wide angle, added to an f=9.7-48.5mm?
Do you think is worth to invest 500 in this accessories than to buy a new SLR?
I do some astrophotography, nature and travel photography for fun and I just want to get closer to the subject reducing or enhancing depth of field.
I'll value your opinion.