This is the 58th most frequent Finnish word.
ensi
"Ensi" means "next" or "first (upcoming)" in English, often referring to time.
In this sentence, 'ensi' is used as an adjective meaning 'next' to describe the upcoming week (viikko=week).
Ensi viikolla menemme teatteriin.
Next week we are going to the theater.
Here, 'ensi' functions to modify 'apua' (aid/help), meaning 'the first' or 'initial' aid.
Annan sinulle ensi apua tarvittaessa.
I will offer you first aid if needed.
In this sentence, 'ensi' means 'the first,' describing the first occurrence of the action.