If you've just got one or two slides to scan, most photo-processing shops (including the counters in big supermarkets) can do the job for you. Howecver the prices charged would be uneconomic if you've got more than a few slides.
For a larger quantity you'll either need to buy a film scanner or to borrow one from a friend. (Some flatbed scanners have a film-scanning facility built into them, so you might not need to find someone who actually owns a dedicated film scanner. However you can't use a standard flatbed scanner as you need a device which can pass light through the slide, rather than simply reflect light off it).
Chris