For online consultation session you have to choose available Veterinarian and put a request for consultation. Of course there are free as well as chargeable sessions, varies with doctors. Generally consultations are done in case of chronic problems like skin problems, obesity etc.
In acute cases you can opt for home visit or clinic visit. In both the cases you have to talk directly with the available doctors over phone. Charges will vary with doctors, distance, kind of problem etc.
For surgical procedures charges will vary too.