It is used for ongoing treatments. For example, "liječenje se može nastaviti" (treatment can be continued) is a common phrase in medical manuals regarding anti-arrhythmic drugs.

Depending on whether you are learning the language or using it in a specific context (like cooking or legal procedures), 1. Language & Grammar Guide

Used to continue doing an action. Nastaviti trčati (Continue running).

The word is a South Slavic verb (Croatian, Serbian, Bosnian) meaning "to continue," "to keep going," or "to resume."