"I am watching TV in the kitchen."
Translation:Yo miro la televisión en la cocina.
"Mirar" already means "to look at".
So I assume using the preposition "a" here would mean "I'm looking at at the TV."
disclaimer: I'm not a native Spanish speaker. Take my opinion with lots of grains of salt.
Mmmmm good point. Spanish Dict uses it in their examples. Perhaps not common in all Spanish speaking countries, so it was not included?
I suspect its just not in the database. Duo has taken "TV" other places for "television".
'Soy' would be for something that applies all the time - like "Yo soy alto" - "I'm tall." (I'm tall, I always am, and I always will be). But if you're describing something that you're actively doing/experiencing that isn't a permanent trait or circumstance, you should use 'estoy', as in "Estoy cansado" - "I am tired." (I'm not always tired, I'm just telling you that I'm tired in this moment)
Estar is used with the present participle to make this tense (present progressive) in Spanish, as I understand it.