Both are possible depending on context.
In this sentence, uso tênis is best understood as I wear sneakers/shoes. Portuguese often uses usar for wearing clothing, shoes, and accessories:
So even though usar literally looks like to use, it is also the normal verb for to wear in many contexts.
In Brazilian Portuguese, tênis can mean both:
In this sentence, uso tênis clearly means I wear sneakers because of the context.
This is a very common word in Brazil for casual athletic shoes.
Portuguese often leaves out the article when talking about something in a general, category-like way.
So:
In this sentence, prefiro chinelo sounds natural because the speaker means footwear in general, not a specific pair.
Para caminhar means for walking or to walk and expresses purpose.
So:
It tells you why the speaker wears sneakers.
Portuguese often uses para + infinitive to show purpose:
Em casa is a fixed, very common expression meaning at home.
The second one usually refers to a specific house, often someone else’s house:
So in this sentence, em casa is correct because it means at home in a general sense.
They are in the present indicative:
Here the present tense describes a habitual action or general preference, not necessarily something happening right now.
So the idea is:
Yes, a little. Portuguese allows some flexibility.
For example, these all sound natural:
The original version is very natural because it starts with the time expression and then contrasts outdoor and home footwear clearly.