"There are three chairs."
But は is a topic marker, and です is a copula. So it would mean "as for [the] chairs, three are", and google translate (not the best source, I know) also translates いすは三つです as "There are three chairs". So if a native speaker or someone with a high JLPT level could clarify, it would be great
Grammatically, a copula is used to link or equate two things, ideas, or properties. In English, 'to be' serves this function; in Japanese, its 'desu'.
In English, 'to be' also serves a non-copular role meaning 'to exist' when used with the dummy subject of the verb. In Japanese, this function is served by 'arimasu' and 'imasu' for inanimate and animate objects, respectively.
In general, if one can replace the 'to be' in an English sentence with 'to exist' without it becoming ungrammatical (e.g., "There exist three chairs" here) then 'arimasu' or 'imasu' are used in Japanese.
For further comparison, Spanish has two copula -- 'ser' and 'estar' -- and handles existence with a third construction, 'hay.'
I found a good explanation here
"desu is sort of like the english word "is", but it is only used when neither iru/imasu or aru/arimasu are used.
By itself, iru/imasu assert the existance of something that is alive.
aru/arimasu are similar to iru/imasu except the assert the existance of something that is not alive.
The number one rule in Japanese is that you should not learn the meaning of Japanese words by trying to put an English word to them. Instead, you should learn them by trying to put situations to them. Here's some situations, and which word you would use in each one.
That book is blue. --- desu
That book is here. --- arimasu
He is here. --- imasu"