Stone - I wasn't trying to be awkward, it's just a bit like someone coming on here and saying 'tell me about deer stalking'!
The things that make your vet suspect meningitis would include head pressing, stiff neck, high fever, depression, head tilt etc. There are wide ranging possible clinical signs.
A quick google throws this site up that looks decent
Meningitis | Meningitis in Dogs | Information on Dog Meningitis
Basically it can be caused by lots of different things, that includes bacteria, fungi, viral, parasitic, auto-immune and unknown causes. The hard part is characterising the initiating cause, this is where it gets tricky (and potentially expensive). Samples of cerebro-spinal fluid will need to be taken and some specialised imaging may be needed (MRI or CT scans). Blood will be taken to see if there has been exposure to certain parasites.
Depending on the cause depends on how it is treated. The treatment for one condition could make others much worse. You cannot feasibly treat for everything.
If there is no money for referral then I have treated speculatively with high doses of steroids and antibiotics but it's a poor man's option. If my own dog had meningitis symptoms it would be off to a specialist.
Maybe if you give us more detail we can give a more accurate picture. Is this your dog? What are the symptoms? What tests or treatment has been carried out?
This is a huge area.