"Yo leo las palabras."
Translation:I read the words.
Contraction. I am vs I'm. Remember that particular English writing teacher? I think its a similar thing here based on other reaponses on here to this subject, and my experience with native speakers.
Duoliingo teaching you a language wants us yo learn the standard way initially, im assuming. It's kay though! As we become fluent we will know when we need to or not use contracted versions of a sentence
The difference between 'I do not' and 'I don't' or
'We will not' vs 'We won't'
In both examples we save words and energy. Its about the way its spoken, and the subtle meanings. Contractions
Like when you insist on something:
"I will be the best at DuoLingo!" vs "I'm gonna/I'll be the best ay DuoLingo"
The first one can be more formal, yet more powerful and clear because you spelled it out and thus showed intention. Where as the second is quicker, less formal, but not as serious and casual and can be seen as more freindly even.
It ultimately depends on the context, but hopefully this clears it up a bit.