Learn Finnish: Moi! Me olemme kahvilassa.

No, you could just say olemme kahvilassa. In Finnish, the verb ending -mme already tells us that the subject is "we", so the pronoun me is optional and often left out in everyday speech.

I know the dictionary form of "to be" is olla. Why is it olemme here?

Finnish verbs change their endings to match who is doing the action. For me (we), the matching ending is always -mme. So the base verb olla (to be) becomes olemme (we are).

Why does the word for cafe end in -ssa?

The base word is kahvila (cafe). By adding the ending -ssa, you change it to mean "in" or "at" the cafe. Finnish attaches endings directly to the end of a noun to show location instead of using separate prepositions like English does.

Where is the word for "the" in this sentence?

Finnish doesn't have articles like "a" or "the" at all! Because of this, kahvilassa can translate to "at a cafe" or "at the cafe". You just have to guess which one makes the most sense based on the context.