When you use говорить/сказать in the meaning of "to say" the person to whom something is being said is in Dative.
Where are all you people getting all this grammatical information from? I cannot begin to make any sense of any of this Russian, I'm afraid. It is all just single words - I cannot detect any pattern at all.
You will need to supplement Duo with another resource to have the concepts explained rather than demonstrated. The only reference to the 6 cases I've seen here is in the section titles. There are many good references I've found on the internet, google "Russian cases" and go from there.
On the website each section has an introductory discussion. I've found them helpful.
I grew up learning it and my mom would correct any gramatical error so you just gotta start putting it to use and talk in russian when you can
What is the link between this sentence and "Time and Numbers"? It seems more related to prepositions or accusative
However, skills are just groups of words. They are not thematic.
Yes. Also, neuter prepositional, which is more appropriate here ("это" just refers to "some stuff" and isn't a modifier before a noun).
Masculine and neuter adjectival declensions are the same everywhere except the Nominative (and Accusative when Accusative copies the Nominative). This also work for most cases of neuter and zero-ending masculine nouns—but no so perfectly because the ending of the dictionary form will matter in the Nominative and Genitive plural..
So what is wrong with the answer "about him?" ob etom just means it? What's the appropriate word for him?