Looking at clipless pedals and shoes and see some shoes advertised as toe spike compatible or not. What are toe spikes? Think I understand cleats for shoes and have a general idea of how they work with pedals. any info is apprecaited

toe spikes are 2 metal spikes that stick out of the sole of your shoe that make walking up steep grades in bike shoes possible. They are a good idea for Mountain biking..unless you live where it is very flat.

so on a mtb shoe the cleats are somewhat recessed to make walking easier but optional spikes can be added near the front of the sole to aid walking uphill?

Exactly.

They mount up au the toes to give extra grip for climbing. They are optional because not everyone who wears MTB shoes needs them (cross-country riders, tourers, etc.).