Learn German: Hier gibt es vierzehn Stühle. - There are fourteen chairs here.

It is just the word for four (vier) directly attached to the word for ten (zehn). Most German numbers from 13 to 19 follow this exact single digit plus ten pattern, which is very similar to how we use the suffix -teen in English.

Why is the word order gibt es instead of es gibt?

The basic phrase for 'there is' or 'there are' is es gibt. However, German has a strict rule that the verb (here, gibt) must be the second piece of information in a standard sentence. Because this sentence starts with Hier (Here), the word es has to swap places with the verb to keep gibt in that second position.

What is the singular form of Stühle and how does the plural work?

The singular form is der Stuhl (the chair). To make this word plural, German adds an umlaut to the main vowel (changing the u to ü) and adds an -e to the end, giving us Stühle.

I learned that es gibt requires the accusative case. Does that affect vierzehn Stühle here?

Yes, whatever exists after es gibt is always in the accusative case. However, for plural nouns, the accusative form looks exactly the same as the nominative (the basic dictionary form). That means vierzehn Stühle doesn't need to change its spelling or endings at all here.