How to add slide numbers to show on each slide
Insert a text container (shape or caption) on the first slide. Insert the system variable cpInfoCurrentSlide in the text, using the X button in the Character part of the Properties panel of that text container. Go into the Timing Properties and set the text container to display for the rest of the project, always on top.
You can also achieve the same by putting the text container on the main master slide.
When I imported a powerpoint, it worked.
But when I used the template, it did not work.
What do you mean by 'template'? If this is a cptl-file... please do not use it anymore especially if it has been created in older versions. There are too many issues with cptl-files. Maybe you mean something else, please explain....