"I don't like to watch the commercials on TV."
Translation:No me gusta ver los anuncios en la tele.
Verbs are neither singular nor plural, they describe an action. In English we change many verbs depending on who is doing the action (is, are, am) and time (will be, is, was) and a couple others that I don't know how to express. I don't know why we change verbs based on who is doing the action, that's probably history of language some place, I just know what sounds right. Spanish includes who is doing the action in the verb (estoy, estamos, está) which is part of why this is so challenging.
I am a student as well, and the following is therefore not a qualified answer.
I don't think that there is a consistent rule. My conclusion from searching language sites on the web is that the understanding of ver versus mirar seems to strongly depend on geographical area. Most people perceive a more vs. less active 'seeing'; but some argue mirar to be active (to watch) and ver to be passive (to see), while for others it is just the other way round. There also seems to be a preference for ver in context with television, independent of active watching versus passive exposition.
"I don't like to watch the commercials on TV." so I wrote "No me gusta mirar los anundios en tv" I was marked wrong because I didn't place la between en and tele. Sometimes learning with Duo Lingo can be counter productive as one loses confidence with the fussy and tricky way things are done. I mean, why not just write in English: "I dont like to watch the commercials on THE tv" if you want the la. Sometimes I find Duo Lingo inconsistent and very frustrating. Certainly not helpful in this instance.
There is so much inconsistency as to when "la" is used before "tele". In some of the lessons "on TV" is only accepted as "en tele" else marked wrong and in other lessons "on TV" is only accepted as "en la tele" else marked wrong! It seems like this is because different people wrote the lessons.