On my own observation; "wieso" is frequently used than "warum"... in "wieso", the person is deeply curious or unaware of anything, clueless, for there are less presence of material/tangible subject, looking for more answers: e.g. "wieso rennst du?" (why are you running?); The person have no idea why he/she was running, either where he/she from or heading to, if he/she was playing or in danger, of he/she was chasing or being chase by someone, etc etc... in "warum", the person is looking for a direct answer, also he must have a bit clue or already presupposed that there must be a particular reason of the matter: e.g. "warum liest du das Buch?" (why are you reading the book?); The person knows what the book is (such as the title and its content), he just need to know why he was reading it (the motive)... I hope this help a bit... =)
The word "das" can mean "the" or "that". Many words have more than one meaning in English too. https://dictionary.reverso.net/german-english/das https://dictionary.reverso.net/english-german/that
There are even times when in English we mght use "this", but in German they might still use "das", even though "this" could be a form of "dies". https://dictionary.reverso.net/english-german/this
There is also a less used form of "that" which is used in certain expressions. https://dictionary.reverso.net/german-english/jene
Wrong! "dieses" = "this"
"that" = "das"
and you could even put "das" for "this"
Of course, "das" can also mean "the".
"Das" is also used in a lot of expressions.
Scroll down past the definite article use and you will find that all the definite articles can be used as demostrative pronouns and keep in mind that German pronouns can be used attributively. https://dictionary.reverso.net/german-english/der