Is the excaust motor the same as the fan ? I do hear the fan and air comes out of the vents but no warm air,but it only works when the thermostat is on the ON position,not auto.

Model number and brand of furnace.

Newer furnaces have 2 blowers or fans. The first step is for the small one that supplies combustion air and pushes the exhaust out the vet to start. The last step is for the air circulation fan to come on once the furnace is going. See thesequenco of operations at https://www.askmehelpdesk.com/heating-air-conditioning/heating-cooling-maintenance-repair-troubleshooting-frequently-asked-questions-58313.html