I presume you are using an all-in-one printer/scanner. The most common file format for images exported from scanners is .JPG although other file types are possible. But your problem is where these images are being saved to. If you look at the settings for your scanner you should be able to specify the folder you would like all these images to go to. If you cannot work it out the manual - which you should be able to download from the maker's web-site - should offer guidance.
As for emailing these images it doesn't matter too much where they are saved to, so long as you know the folder you have them in. The emailing procedure is exactly the same - generate your email, click on attach, navigate to where the file is, open the file, it's attached. You did say 'computer' not 'tablet'. On some, even most, tablets the sequence is slightly different.
Paint is a small graphics application built into Windows, it is not a storage location, but if you have no other graphics applications on the computer it may be the default for opening files of .JPG type. 'Scanned documents' sounds like a folder name, possibly in 'My documents', but it is simply a convenient place to put these files. I don't understand what you mean by saying it has 'an email program'.