na początku ?:

1. in the beginning

American english word "na początku"(in the beginning) occurs in sets:

There's no turning back now.
Korepetycje cz. 2

2. at the begining

American english word "na początku"(at the begining) occurs in sets:

Przydatne zwroty do rozprawki maturalnej
Time adverbials
Marcin_7th Sept