questions on japanese word pairs

Hi

I have a teaching book for Japanese, but it doesn't really explain the differences between the following pairs/triples of words. I'd be glad if someone could explain me some of them.

ya << to <> shi "and"
demo <> keredomo <> ga "but"
dô <> ikaga "how"
koto <> mono
koko ni <> koko de "here"
kata <> hito "human being"
naze <> dôshite "why"
doko e <> dochira "where to"
totemo <> domo "very"
dozo <> onegai shimasu "please"
ii <> yoi "good"
hanashi <> hanasu <> hanasu koto "speak" (besides: when are forms like hanashi used?)
da <> de (wa) <> na "to be"

ya << to <> shi "and"
"ya" lists an incomplete group of things (implies there are other things too which are not explicitly stated)
"to" lists a complete group (all elements explicitly stated)
"shi" is used after phrases (not individual nouns), indicating an incomplete listing of reasons for something.
demo <> keredomo <> ga "but"
"demo" - this is actually the "TE" form of da/desu plus the particle mo, so it's actually more like "even so" or "however"
"keredomo" - this is a pretty polite way of saying "but"
"ga" - is a conjunction meaning "but"
dô <> ikaga "how"
ikaga is more polite.
koto <> mono
these are difficult because each word has various uses, some of which overlap.
koko ni <> koko de "here"
"koko" is irrelevant here. The hard thing about particles is that what they mean varies slightly from verb to verb, it's not just a question of what comes before the particle.
kata <> hito "human being"
kata is more polite
naze <> dôshite "why"
basically the same, but "doushite" can also mean "how" in spoken Japanese.
doko e <> dochira "where to"
dochira is more polite
totemo <> domo "very"
probably shouldn't think of these as a pair, even though they are very similar in meaning. There's so many other words that also mean "very": Alternatives to saying totemo | nihonshock
"doumo" is literally something like "no matter how/what", doesn't fit everywhere that we would use "very" in english. It also is used to mean "thank you".
dozo <> onegai shimasu "please"
"douzo" invites someone to do something (which benefits that person)
"onegai shimasu" is the speaker requesting something which benefits the speaker.
ii <> yoi "good"
"yoi" is the form that is used when conjugating "ii", you can use it instead of ii (un-conjugated), but it sounds a little old-fashioned. common in anime/manga.
hanashi <> hanasu <> hanasu koto "speak" (besides: when are forms like hanashi used?)
too big of a topic to answer here, sorry...
da <> de (wa) <> na "to be"
not sure exactly what you're asking here. da is the "to be" verb, "na" is the form of "de aru" that precedes a noun, but you mostly only see it in na-Adjectives. "kirei da" + "hana" = "kirei na hana"
de is sometimes (not always) the TE-form of "da/desu/de aru"
Hope this helps!

Thanks, most explanations are helpful to me

Remaining questions:
1. Is "keredomo" used in the same way as "ga" (before the comma)?
2. Do you know where I can find something about
- forms like "hanashi", and
- how to use "koto"?

1. Yes, "keredomo" typically precedes a comma. Note that this word is often shortened to "keredo" or "kedo"
2. Let me actually try and answer your question this time, the first time I read it I wasn't totally sure what you were asking but I think I get it now.

hanasu = verb
hanasu koto = verb converted into a noun using "koto" (which means "thing")

hanashi is a noun but it's kind of unique. In many cases it's possible to use the ~I form of a verb as a noun (kind of an advanced topic), but in the case of hanashi it's less the ~I form of hanasu and more like its own word altogether. When it's written we just use the kanji 話, we don't write the し.

So basically, think of "hanashi" as a different word, rather than a form of "hanasu", but be aware that in the future you will find the ~I form of verbs being used as nouns.

As for Koto and Mono, the common explanation of the difference is that koto refers to intangible "things" and mono refers to tangible "things". The various grammatical uses of koto and mono can be a pretty advanced topic, which I don't think you need to be too concerned with right now.

Here's a link for various usages of mono, though I don't have a good link for koto. Lesson 85 - IMABI