To express a habit or routine like just "I eat dinner"(at x PM), you could use either "Yo ceno" or "Yo como la cena" (a las x PM). I think this latter would be less used.
Yo como cena is not used at all.
It is heard this form too "Como a eso de las 2": "I eat (lunch, presumably) at about 2". And perhaps "Estoy comiendo a eso de las 2", even though he/she were not eating at that moment, and saying that as expressing a routine part. That would be I usually eat at about 2
"a eso de": http://es.bab.la/diccionario/espanol-ingles/a-eso-de
On the other side, I read that dinner means
main meal of the day usually eaten in the evening or in the early afternoon.
In some countries, the main meal is said to be eaten at about midday, in such cases, would "dinner" be "almuerzo"? or inversely, almuerzo considered as main meal would translate dinner... :)
Could you readers say what time in their countries is eaten the main meal at?
Almuerzo is the meal in the middle of the day i.e. lunch and cena is the meal in the evening i.e. dinner. There size isn't important, the rough time of when you eat it is. Just as for breakfast you could have an apple or you could have a whole pizza, it's still breakfast because of when you have it.
I've never heard any other Spaniard refer to the midday meal as anything other than almuerzo. The same for the evening meal and cena.
I think that's right. While in English "the dinner" is used as a phrase for a particular event - eg a renunion dinner and you might say "I went to the dinner" you would never say "I eat the dinner".
For those curious, in English "dinner" was used quite widely for the main meal of the day whenever it was eaten. Hence the midday meal at school was called the "school dinner" because there was an intention that it be substantial. However the word dinner has, in many dialects, replaced other terms for evening meals (eg "tea" or "supper") because many people started to eat their main meals in the evening.
I frequently buy frozen boxed meals for convenience and I might have some breakfasts, lunches and dinners in my freezer. So I might say "I will eat the dinner now" with reference to a particular packaged meal. Normally, however, I would not include the definite article.
In my part of the country (middle USA) any meal in the morning is breakfast. Lunch is always at mid-day, no matter what the size, but it is usually smaller meals like sandwiches, salads, soups, etc. Supper is always in the evening, no matter what the size of the meal. Dinner can be mid-day or evening, if it is the main meal. So one might have breakfast, dinner and supper - or breakfast, lunch and dinner.
The basic verb is 'comer' (to eat). The general rule is, you drop verb endings and "conjugate", i.e., add a suffix corresponding to the person/number. So, The "first person singular" (I'm assuming you're familiar with person and number) ends in -o, giving como. The list is as follows:
Yo como. I eat. Tú comes. You (informal) eat. Usted come. You (formal) eat. El/Ella come. He/She eats.
Nosotros comemos. We eat. Vosotros coméis. You (informal, plural) eat. Ustedes comen. You (formal, plural) eat. Ellos/Ellas comen. They (male or mixed group)/They (female group) eat.
Note that 'comer' is a verb ending in -er. There are similar rules for -ar and -ir verbs.
Because its Spanish. that's the main reason. We could contrive a possible situation in English: A selection of cards passed around at dinner time and everyone's card says something different. The waiter asks individually: John, what do you eat? John replies, 'I eat the dessert'. because his card says dessert. Mary's card says 'salad' and she says I eat the salad. So,now, Larry's card says dinner. So how should Larry reply to the waiters inquiry? Yes, of course, I eat the dinner. There you have it. Quite contrived albeit. Agreed. Weird