Creating captions in Premiere Pro is easier than ever with the recent updates, which introduced a Captions workspace. To start, open your Premiere Pro project (or import your video into a new project) and select the Captions workspace.
On the left, you will see the captioning workspace that you will be working in.
Create a new caption track by clicking the button or using Command+Option+A, and select the subtitle format. You are now able to add caption track segments, either by clicking the plus sign at the top of your caption workspace or by using Command+Option+C.
As you add caption segments, you can double click each one to change the text within the text panel. If you double click the caption on the video preview, you are able to change the positioning, style, font, etc. with the edit tab of the Essential graphics panel.
If you need to adjust where a caption segment begins or ends, you can click and drag the edges of the caption segment in your timeline like you can with any other video clip, image, or text as per usual in Premiere Pro.
Once you are happy with your captions, you have a few options. If you just want a standalone .srt file for your captions which you can upload alongside your video on a platform like Youtube, you can click the elipses in the text panel where your captions are and select Export to SRT file.
Alternately, if you want to burn the captions into the video, that can be done via the export feature. When exporting your project to a video file, the default option selected is to burn the captions into the video. If you do not want to burn them in, you can navigate to the captions tab in the export window and change it to create a sidecar file instead.