Click then type ID in chat.
Example: DIAMOND, STONE, COAL,...
Click then type data (custom model data in 1.14+) in chat.
Example: 1,3,5,6,2,...
Click then type display name of material in chat.
Example: &eTest Material
Click then type base on format: <line> <lore>.
Example: 5 &eLore in line &45
Click to change value.
Click then /forge reload and see it in /forge material