There are sentences where nouns do not have articles; for instance after the preposition "la" you often do not use an article. Nevertheless, Romanian generally uses the definite article more often than English.
Same as in Italian: "io mangio IL pranzo" (I eat the lunch), where pranzo is a noun; you can't say "io magio pranzo". If you don't want to use the article, then you have to omit the verb "mangiare", hence "io pranzo" (I lunch). Pranzo becomes then a verb (pranzare).
"Mangio" looks like "mange" from French. What a nice language family we all share. By the way, after I finish French, Romanian, and German, Italian is next as my 7th language (holy smokes!). It's a beautiful language.