What it means
Closed captions are a selectable text alternative for a media recording. They represent relevant speech and non-speech audio. The player lets a viewer turn a caption track on or off; open or burned-in captions are part of the visible picture.
Captions are more than dialogue
A useful caption track can identify a speaker or a meaningful sound when a viewer cannot infer it from the picture. For a fictional example, [door closes] may explain why someone turns around. Decide what the audience needs in that scene rather than adding an identical sound label everywhere.
A file is only part of the workflow
A sidecar SRT or VTT needs to be associated with the intended recording and exposed correctly by the player. Converting formats does not add missing sound information, correct recognition mistakes or prove synchronization.
Use the converter for an appropriate plain-text format and the reading-speed checker for cue-level review. Then watch and listen to the recording, check the wording, and test the player's caption control.
Common mistake
Burning words into a video and supplying a selectable caption track are different deliverables. State which one you have made, and preserve the editable text and timing when possible.