I have added to my iPhone a new album which includes explicit music. When I check on iTunes I can see the music is on my iPhone, but when I search for these songs on my iPhone I can't find them.
What do I have to do to make this album visible?
One thing you could check is whether Resrictions are enabled on your iPhone.
To do this:
NOTE: If you get to Step 5, the restrictions passcode is most likely not the same as your iPhone's normal passcode. So if you try entering that and it doesn't work, do not keep trying to enter it. Instead you will need to speak to the person (e.g. a parent) who would have enabled restrictions to begin with.