Ringworm is a highly contagious infection that can affect a variety of different animals with a variety of symptoms, and yes it can also be caught by humans too directly from dogs or the specific animal that is infected.
The cause of the infection is due to organisms (which are actually a fungus) called Dermatophytes which start by affecting the skin on your dog.
The fungus can also come in a variety of different forms including Microsporum Canis, Microsporum Gypseum and Trichophyton Mentagrophytes.
The Symptoms of Ringworm The symptoms of this infection can include:

• A loss of hair is specific areas.
  
• You may notice that your dog starts to get lesions on the skin
• Due to the fact that the fungus which causes the condition actually live in your dog's hair - when the lengths of hair break off near to the skin this causes a loss of hair
• Your dog's skin may appear red and itchy in places
• The famous 'Ring' is caused when the lesions get bigger and make a circular appearance with a scaly crusty centre
• The patches of baldness way spread to cover more areas on your dog's body
• The skin may appear very dry and crusty - but this expected with this infection
• The symptoms of the condition are very similar to Scabies (Mange) and your vet will need to examine your dog to get an accurate diagnosis.
  

The Treatment for this condition may include:

• Anti-fungal medication
• Anti-fungal medication will be used as a topical ointment to be applied to affected areas - the most common type also uses a culmination of a shampoo that uses 2% Chlorhexadine in the ingredients.
  

Canine Ringworm can be treated quite effectively but remember that it is highly contagious so you may catch it too if you are not careful.