"We don't understand this grammar lesson."
Translation:Nous ne comprenons pas cette leçon de grammaire.
Ce - masculine singular. Cette - feminine singular. Ces - plural. These are adjectives attached to a noun, meaning this or that. However ce can also be a pronoun, often seen as C’est or ce sont at the beginning of a sentence. Ça is a different word, short for cela. It’s a pronoun and stands by itself, not qualifying a noun. https://www.collinsdictionary.com/dictionary/french-english/ce
Ce → demonstrative determiner masculine singular
Cette → demonstrative determiner feminine singular
Ces → demonstrative determiner plural
Ça → indefinite demonstrative pronoun
→ Ce chien est gros.
→ Cette maison est rouge.
→ Ces enfants sont grands.
→ J'ai besoin de ça.
▶ Link: Demonstrative Pronouns and Determiners in French on lingolia
I've been asking this in several forums, and it says that if you have a noun acting as an adjective, you need "de" however, I'm still very confused because they're all adjectives describing the noun, and always should have "de." I still do not understand why "de" would ever need to be dropped, and more importantly, how you know whether to add "de" or not.