Looking for some very basic advice, please! I recently moved into a new home which has speakers built into some of the rooms.
Not sure what 'some of the rooms' means.
The first thing to do is figure that out. Figure out what and where speakers are and what wires they are connected to. The best way to do this is to read the clearly marked labels on the cabling. If there are NO labels, then that speaks volumes about the quality of the work which was performed. I mean, if it goes into a wall and disappears, how the heck will ANYONE know where it goes to without proper cable labels?
There are plenty of ways to identify where a speaker cable is connected to, and there are videos on YouTube about this.
ie:
Find where those speakers go, THEN LABEL THEM!
Then make a list of every speaker in your home, if it has been identified, and if there are any speakers or wires leftover that have become ghosts. This does happen in homes from time to time when poor wiring was used or certain areas have been removed or not installed. I have several zones in my home with speakers that I have not yet installed. Maybe I never will. I know they go up to my attic, but for the most part, they are 'ghost' cables because they aren't connected to anything at this time. It happens, and isn't something to worry all that much about.
If you are unsure of all of this, you can hire an AV professional and they should be able to come in and identify and label everything for you in a few hours. May cost a couple hundred/few hundred bucks depending on the complexity of the previous system and how well (or poorly) it was installed.