When do we use adj. before noun and when do we use noun before noun to make compound noun? E.g: We say: theory lesson or theoretical lesson
adj. or noun.
adjectives describe nouns - nouns are words used to name a person, animal, place, thing, and abstract idea.
- you can use an adjective before a noun like this:
She was wearing a beautiful dress for her cousin's wedding.
- you can use an adjective after a noun like this:
The dress she wore for her cousin's wedding was beautiful.
as for your questions whether is should be theory lesson or theoretical lesson - it should be theorical lesson since theory is a noun, not an adjective. Theoretical is adjective that describes that the lesson is theoretical in nature.
just to keep it simple:
remember: what is being described (noun) and how the noun is described (adjective)