"Yes, this is nice!"

Translation: Ano, to je hezké!

[BoneheadBass]

Have a look at the Tips and Notes for To Be-Singular and To Be-Plural. (I think these are only available on the web version for now, though.) Or you could click the link for 12. Irregular Verbs here: https://en.wikipedia.org/wiki/Czech_conjugation.

[Karel400144]

In the rest of the course is "to" translated as "that".

[VladaFu]

Nope, even in the very first lessons we have To je/Je to as This is/That is/It is.

[AgnusOinas]

When it's actually a demonstrative modifying a noun, such as "to dítě" or "to pivo", that yes, that's always "that" or "the", never "this".