Hi
As one newbie to another I'll try to allay your fears. You could also download the free 30 day trial and explore the issues. I am currently running the trial version. Its easy to download and install.
All my image files are held in a logical file structure with just one folder at the top level. It was a simple process to point LR at the top folder select 'all photos' and import all the images. This takes a while if you have lots of images, but you could do it with a smaller subset for a quick tryout though.
Having imported all my image files into LR, my folder structure and all my files are just as they were. Nothing changed, apart from the fact that LR has added its catalogue (folder structure containing its database files). It hasn't messed with anything I had before though.
I can still find all my files using the file manager (windows explorer in my case) - nothing has moved. I can still edit them with other converters or editors if I want to.
If I now move files within my folder structure outside of LR I will cause LR a problem since it only knows where they were when imported, but its not difficult to fix that.
So for example I can still use Bibble 5 to edit RAW files (it saves edit data in sidecar files, which LR doesn't use in its default configuration) . See post by TNG below.
Changes made in LR are stored in its database, so changes made by either of these are not seen by the other. LR uses the same method for JPEG & TIFF files so these changes are also non-destructive wrt the original file.
To get some output outside of LR you do need to "export" but this is really just LRs term for "SAVE AS" to produce a jpeg or tiff. In Bibble you use an "OUTPUT" batch dialogue. So for example if after working on a folder full of images you wanted to produce a number of jpegs to print your favourites you'd click on "Export" from the file menu, make selections for format (jpeg), where you want them, what output sharpening etc, and click the Export button (I think its labelled export).
If you tried LR for a month and having imported all your images, and exported some as jpegs, you then decided not to go for it. All you would need to do is uninstall it delete the catalogue and your images and file folder structure are as they were. Unaffected. (except you might have some new jpegs or other output (exports).
You are kind of locked into it once you invest time in editing many images because the image adjustments and the catalog (asset management) facilities can only be accessed by lightroom. Your output (exports) though have the benefit of those adjustments so the jpeg, tiff and dng files are a permanent record of the final result. That pretty much goes for any other solution though.
Regards
John