Řadové číslovky

Ordinals are "first, second, third". In English they never change; in Czech they are adjectives and agree with the noun in gender and case, exactly like nový or moderní.

The forms

První and třetí are soft adjectives: one form for all three genders, první den, první cena, první patro. All the others are hard and change: druhý den, druhá cena, druhé patro. And they decline: Bydlím ve třetím patře - I live on the third floor.

The dot is the "-th"

English writes 28th; Czech writes 28. - the full stop after the digit is what makes it an ordinal. So 5. patro is "the fifth floor" and Karel IV. is "Charles the Fourth" (Karel Čtvrtý). Read a figure without the dot and you have a plain number; read one with the dot and you need the ordinal.

Dates

Dates use the ordinal in the genitive, the case for "of": prvního ledna (on the first of January), pátého května. Two dates every Czech knows: 28. října (dvacátého osmého října), the founding of Czechoslovakia in 1918, and 17. listopadu (sedmnáctého listopadu), the start of the Velvet Revolution in 1989. Ask Kolikátého je dnes? - literally "the how-manyth is it today?", a word English simply lacks. The answer: Dnes je dvacátého čtvrtého prosince - today is the 24th of December, Christmas Eve.

Up to a hundred, compound ordinals turn every part into an ordinal, where English only changes the last: 21st is dvacátý první, not *dvacet první.

Which floor?

Czech counts floors the British way. The ground floor is přízemí, and první patro is one floor up - what an American calls the second floor. If your Airbnb host in Brno says ve třetím patře, that is three flights of stairs.