This is the 136th most frequent Serbian word.
првог
"Првог" means "of the first" in English.
The word 'првог' describes the ordinal position (first) of the noun 'такмичења' (competition) in a genitive case context.
Данас је дан првог такмичења.
Today is the day of the first competition.
In this sentence, 'првог' describes 'дана' (day) in a genitive case because of the preposition 'од' (from), which demands it.
Учествовао је од првог дана.
He participated from the first day.
Here, 'првог' specifies the ordinal position (first) of the noun 'путовања' (trip) and is used in genitive case as required by the verb phrase 'Сећам се' (I remember).