Standard or stack-able concrete block can be stacked dry and then coated with a surface bonding cement. Surface bonding cement contains fiber and acrylic and polymer fortifier. More traditionally concrete block are set in mortar. When concrete block walls are set in mortar some of the cells be filled with a slurry mix, mortar, and concrete depending on local building code and height of the wall. Additionally steel rebar can be inserted. After spreading the mortar the end of each block is buttered and then set into place
Once the block is set in place it is leveled. Next another block it buttered and set into place.
A lead is then constructed and a line stretched out between the two independent leads
The space between the two leads is then laid on block at a time, wire and reinforcing can bet laid between the coarses for added strength. Check your local building codes.
Larger walls can be filled with concrete and Rebar