Okay so if u have a DSLR u will have the option to shoot in RAW, JPEG or RAW+JPEG. Most people shoot JPEG because they recognise the file type and have programs that can open JPEG. Ill not go into it too much explaining the difference but heres a easy way to think of it.
JPEG: Smaller file type.
Is like loads of paper thats been laminated, theres loads there but its finished and finalised, u cant change or re-order them.
RAW: Big file type.
Is loads of paper waiting in a laminating pouch, theres lots of paper that can still be edited and reordered before finalising it and laminating it.
So if u shoot RAW u end up with a NFO (i think its called) which only new versions of photoshop or lightroom can open.
Now when u shoot in manual settings mode like i do (auto is for point and snappers not real photography) you sometimes get the shutter speed or exposure wrong. So you might end up with a very dark or very light picture off letting too much or too little light in.
Heres one of the fabia that i had the shutter speed far too high when i was busy working out what settings were best to use:
So, as u can see its pitch dark and can barely make out the car.
The next pic is the same picture but with the exposure settings changed in lightroom to brighten it up so you can see the picture. Even i didnt think it was possible to bring a picture from basically a fuck up to the final edited picture.
I changed the white balance a bit as i like the yellow/orange tinge to a picture as it looks a bit better with sunset pics in my opinion and the above picture is very low quality as the finished file is 63mb and wuda took ages to upload. So the pixelated bits on this aint on the proper full size picture its purely to show u the amount that RAW and Lightroom can do for your photography.
Everything i have learned in photography have been from "FroKnowsPhoto.com" and watching his videos on youtube, search for "JaredPolin" and i watched every tutorial he has over the space of 3 weeks to get where i am now so he defo worth a watch as he explains it all in language anyone can understand.
Hope that all helps