SRT files contain subtitles for video files. If you have downloaded a video, and an SRT file came along with it, you don’t need to keep the SRT file if the video is in your language. The video will work fine without the SRT.
How you use the SRT file depends on what video-player software you are using. For example, with VLC, all that you need to do is drag-and-drop the SRT file onto VLC as it is playing the video and it will automatically start showing the subtitles. The same is true for Media Player Classic which comes with the freeware K-Lite Code Pack.