Not really my area of expertise, but...
A dedicated line could run from say your warehouse on the other side of town, to your office. The line is there 24/7 for your exclusive use. It can be for data and/or voice, and usually you'll rent it on (probably) a yearly basis, so you pay the same if you use it for 5 minutes just once a day, or every minute of every hour! Dedicated lines can be over short distances, intercontinental, via satellite, etc.
A switched line is not exclusive to you. It will possibly be part of the PSTN, and just possibly could be "busy" on occasions, i.e. in use by other people or services. You would generally expect to pay for your timed usage of the line, so using it just once a day for 5 minutes would be cheap compared to using it solidly all day long!
I believe that's it in very basic terms. Hope that helps...
ROGER - GØAOZ.