i'm not sure what a 'A75' is lol, but hopefully i can help..
i touched base with the manual and exposure settings for the first time only a few weeks ago and i was deeply impressed.
+ means brights (the shutter stays open longer and it lets me more light meaning more detail and a brighter photo)
- means darker, (opposite of what i said up there ^)
ISO, i'm not sure what it does but i always leave that on auto haha
if you're taking photos at night, maybe a tripod would be a wise investment
then put the exposure to +2, (because +2 will leave the shutter open for a longer time to allow more light in, it will also be harder to keep the photos from blurring, so holding it still will be a mission in itself, so i tripod will fix that)
also, if it's anything like my IXUS 30, u can 'white balance adjust' mines auto, i just select that option and it will pause for a moment and adjust to what it see's. maybe that would work for dark scenes?
i'm not sure, my suggest above all would be to go out.. and f**k around with the camera lots, try the same shot with every setting, and then play around with the manual settings, see which works best 
also, are u ONLY looking at them on the computer? maybe print them out and see how they work, it may be that your monitor is too dark :\
i dunno, hope i helped, even if just a bit.
-matt