Hello Sekula And welcome to the Polish Forum. There is quite a bit on here in the genealogy sections and if you type key words into the search box, at the top right of this page you should find something to help you.
SekuĊa was probably derived from the Latin soecula (centuries, ages) as in the prayer: Per omnia soecula soeculorum (translated in English as world without end, literally: over all the ages of ages). There were cases where fragments of Latin prayers (Vobis, Meus, Dominus) served as nicknames for people associated with the parish (sexton, sacristan, bell-ringer) and these eventually evolved into surnames.