Translation:This coat is ideal for hot weather.
I agree! "Le manteau" is a substantial coat, not something you would wear on a warm (much less a hot) day. It would be better if Duo introduced the concept of the jacket: "la veste" (for men) and "la jaquette" (for men or women). http://www.larousse.com/en/dictionaries/french-english/jaquette/44673 Then there is the leather jacket, "le blouson de cuir". ;-)
In France "la jaquette" is not a jacket for women.
It is a man's jacket with the back longer than the front.
in this cas, it is "par".
but you could also say "ce manteau est idéal pour l'été" or "... pour des températures douces".
"par" is a preposition which can mean different things, according to context, most often it means "by".
"par temps chaud" does not translate directly in "by hot weather", the English use preposition "for".
"for hot weather" does not translate directly in "pour un temps chaud", there is no grammatical reason for that, it is just that expressions like these ones do not match from one language to the other.
"par temps chaud" is a fixed expression that you cannot change. If you don't use "temps chaud" you can indeed say something like "ce manteau est idéal our les hautes températures".
Otherwise, if you want to use preposition "pour", you have to add a verb : "ce manteau est idéal pour sortir par temps chaud".
In other words, preposition "pour" here would introduce a verb.
This may be similar to the English “by day” and “by night,” where the “by” means “during.”
ce (or cet if followed by mute h or a vowel) = masculine
cette = feminine
ces = plural
They are all demonstrative adjectives and are used with a noun ("cet homme est gros").
ça is a pronoun - used instead of a noun ("ça va bien")
Note that "ce" is also a pronoun and is used (instead of ça) with the verb être ("c'est", "ce sont"). In this sentence, "ce" is an adjective though.