Hi
You don't say what version you are using but this is the sequence of steps to use to add a subtitle in V2.12 (Free)
Open VP and add a clip or clips to the media list.
Drag your clip or clips to the sequence, line.
On the left hand side of the screen click the "Subtitles" button which will open the subtitles window with a preview of your film.
Use the "Play" button (>😉 to run your film to the point where your subtitle is to appear, or you can drag the red line along if you like.
On the left hand side enter your subtitle text into the "Subtitle text" box.
It would be nice if the "Start time" box automatically filled with the red line cursor position (shown on the right under the preview window) but it doesn't, neither can you cut/paste it from here so you will just have to enter the time shown manually.
Now enter the duration in seconds that your subtitle is to show.
Now select font and size and colour for the subtitle.
With these values entered click the "Add + Continue" button.
Your subtitle text will now display in the list window on the lower left of the screen with the start/finish times.
You can play the film in the preview window (or drag the cursor line) to check your text looks OK.
You repeat the procedure for further subtitles. (or "Add +Close to finish)
You can save your subtitle list and load it again for later editing.
Hope this helps.
Nat