Look up this word
volunteer

In a sentence
Nie som dobrovoľník.
I'm not a volunteer.
Som dobrovoľník.
I'm a volunteer.
Examples from Tatoeba (CC BY 2.0 FR).
Source
Slovak National Corpus (SNK) ↗English gloss from the frequency publish path. Example sentences from Tatoeba (CC BY 2.0 FR).
Full attribution on References.