How do I correctly import images into Lightroom?

Question

Before installing Adobe Creative Cloud, I deleted Adobe Elements and all files in My Pictures on my hard drive so I could start fresh. I copied groups of images from CS5 Bridge on my old pc onto an empty flashdrive and tried to import them to Lightroom. In addition to those copied images, whole bunches of other images imported. Even worse, those added images were sorted strangely, not even belonging to the groups as I had them in my old pc.

Answer 1

Since you used the Copy import type, at least the images are also where they originally were, other than those on the flash-drive which was a temporary location for images from another location except when you plug it in.
So there seem to be two unexpected things: more images were imported than you wanted to be imported, and some of the images are in folders that don't match the date they were taken.
The folder-date mismatch might be due to some of the photos not having a taken-date in the exif information so the date they were last modified is used, instead.  You should check your destination naming options in LR to see if you have things set to import into date folders or not.  If not, then you actually specified that LR import a particular import's photos into a specifically-named folder that you typed the name of.
As far as how extra photos got imported, only you can answer that.  It would have to do with where you told LR to import from and if you have Include Subfolders selected.  There is a way to specify an Auto Import folder using LR / File / Auto Import where LR will watch for photo files and import photos it see show up in that folder, but I doubt that is the problem.
You'll have to decide on what to do now.  If you have all the photos still on the flash drive, then you might want to start over.  However, also think about if you want to be doing a Copy Import into your pictures folder from everywhere else, or if you want to use Explorer to copy the photos, yourself, outside of LR and do an Add import.  A Copy import from the flash drive could make more sense, since that is only a temporary location for the photos, but for other photos already on your computer, an Add import might make more sense.  If you use your OS copy commands to move photos from the flash drive to your computer's internal drive, you can decide what to name the folders, instead of LR choosing, if you have LR Import set to use dates.
If things aren't in completely the wrong places, you can drag-and-drop within the LR Library Folders panel to put things where you want, and you can also right-click Remove (without deleting from disk) any extra photos.
Also, there is nothing magic about the Pictures folder.  You can choose to make a new folder and put your LR photos under it. 
The bottom line is that LR isn't doing anything more than what you told it to do, and it sounds like you just aren't aware of all the settings enabled during your imports so unexpected things happened.