1) The first sentence can be revised to:
Robinson enslaves Friday, giving him the name "Friday" due to the day he was rescued.
To achieve this, you can change the phrasing to emphasize the action of enslaving Friday and reword the reason for giving him the name "Friday."
2) The second sentence seems correct:
The book includes specific references to the names of countries, streets, and towns, and also provides detailed descriptions of the interiors.
No changes are necessary for this sentence.
3) The third sentence can be improved:
Using the pen and ink he finds on the ship, Robinson starts writing a diary to maintain a connection with his homeland.
In this revision, the verb tense is changed from "has found" to "finds." Additionally, "an ideal contact" is changed to "a connection" for clarity.
4) The fourth sentence can be rephrased:
The writer needed to use a simple writing style to ensure that even less-educated readers could understand.
The revision clarifies the intent by explaining why the writer needed to write in a simple way, rather than just stating that he had to.
5) The fifth sentence needs a small adjustment:
He starts a goat farm because he realizes that his supply of gunpowder is running out.
Simply remove the apostrophe from "goats' farm" to correctly pluralize "goat farm." The reason for starting the goat farm is clarified by mentioning Robinson's dwindling supply of gunpowder.
Overall, your sentences are clear, and with minor adjustments, they will be even more precise in conveying the intended meaning. Great job!