Learn Finnish: Onneksi me pysyimme teltassa. - Fortunately, we stayed in the tent.

The dictionary form is pysyä (to stay). To form the past tense, we take the stem pysy-. Because it ends in the short vowel y, we simply add the past tense marker -i- right next to it, giving us the past stem pysyi-. Finally, we attach the "we" ending -mme to get pysyimme.

The word for tent is teltta. Why is there only one t in the middle of teltassa?

This is due to consonant gradation, an earlier rule you have likely seen before. Adding the -ssa (in) ending closes the syllable. This weakens the strong double consonant -tt- in teltta into a single, weak -t-, resulting in teltassa.

How does the word onneksi translate to "fortunately"?

It is built from the noun onni, which means "luck" or "happiness". By adding the -ksi ending (the translative case), it turns the noun into an adverb that translates to "luckily" or "fortunately".

Could we drop the word me and just say Onneksi pysyimme teltassa?

Yes, absolutely! Because the verb ending -mme already tells us that "we" did the action, the pronoun me is optional. You generally only include it if you want to add emphasis.