In this case, in English you wouldn't say "I'm dinnering" , instead you use a different verb like have a dinner or even dine. However, you say "He has changed his attitude" and also "That was a big change". "change" can a verb and also a noun, right? In Spanish, cenar means to dine or to have dinner, and it's a verb, and one of the conjugation of cenar is "cena" (mi madre cena, la chica cena...) and it's noun form is "(la)cena", that's why so confusing.

Estoy cenando is I'm dining or I'm having dinner.

La cena está rica is The dinner is delicious.

I hope this will help you.

Thank you. These explanations make sense. I have to be careful mixing nouns and verbs and understand the context of the sentence.

This was helpful :)

It's not a noun. As you correctly said, they are not conjugated.

"cenando" is the gerundio form of the verb cenar.

"Estoy cenando" means "I am dining", like you could express with the English present continous tense.