Whats the difference in a Handheld CB /Handheld scanner?

A handheld CB is just that, a CB transciever that you hold in your hand. It could be a 40 channel 5 Watt radio, or a single channel 100 mW toy. Sometimes these were called walkie talkies. They are designed to work on the CB frequencies (26.965 to 27.405 MHz), and allow you to receive and transmit. A handheld scanner is a just a receiver, but it is designed to work over a very broad frequency range. Most older handheld scanners work from 25 to 512MHz. Newer handhelds scanner will work to much higher frequencies. You need to figure out what you want to listen to, find out how that is being broadcast, and buy an appropriate scanner. The weather band is a VHF band between 162.4 and 162.6 MHz. The National Weather Service broadcasts continous weather on the frequencies. Not sure what you mean by 3 or 10. Could be weather channels. Older unit only had maybe 3 weather frequencies, then the US added 4 more for a total of 7, and the Canada has a few more, that might make 10. If you mean channels 3 and 10 on CB, theses are specific frequencies.

A CB is a Citizen's Band Radio which you can use like a walkie-talkie on 40 channels. Most truckers have CB's in their trucks to talk to eachoter while driving. Depending on which state their in, they usually communicate on channels 1 or 19. A handheld scanner is for listening only. You cannot communicate on it. You can receive frequencies like air-traffic, old police channels, contruction and racing radios that are not encrypted etc. Some will allow you to scan analog cell phones and cordless phones. Weather bands are used for boats and light planes etc.. Basically it's a continuous weather report on AM frequencies. Hope this helps!