"Bohemia is in Czechia."
Translation:Čechy jsou v Česku.
You're correct. Bohemia is a historical region in the Czech Republic. In Czech, it is called "Čechy". The other name used in the above sentence "Česko" is short for "Česká republika" and refers to the whole country (ie. not just Bohemia, but also Moravia and Silesia).
Čechy = Bohemia
Česko = Czechia
Depends on the word and its use in the sentence. You should review the Tips & Notes for the early Skills for details. T&N are available ONLY from a desktop or mobile browser, not currently in the apps. Click on a Skill circle ad you will see a Tips button if T&N have been released for that Skill. If it's there, clicking on it will take you to the T&N.