Audio Wiring Question/Help please ;)

Sorry i have a lot of questions haha

just took my head unit out to find this behind it..

I have a 2001 nissan micra k11 activ 1.4 16v if you need to know for wiring or anything i have next to no clue as this is my first car, why are these two cables cut and what is it making me miss out on? also what do i need to buy in order to fit an aftermarket head unit.. i think this is already aftermarket but its crap so need a new one i assume this adapter will fit any other stereo any help is much appreicated thanks guys

Usually 1 blue one is remotw power to turn on amp maybe the other one could be power for antenna? What radio is it? You should look for diagram online
If it's still got the iso connector a new after market stereo should just plug in. You'll have to mess about the the lives (yellow/red) to hold memory. Oh and the earth (black) on mine was not on the plug but bolted to the inside behind the dash!
So if you plug it in and f@@k all happens you need to connect the earth separately.