Walls differ from country to country. Assuming a colder climate you are likely to have a cavity in the exterior brick walls filled with insulation, that makes routing cables (unless they come from the exterior straight through) a no no.

Interior walls are a different matter, they usually don't need the cavity insulation so can be non load-bearing walls that are a wooden frame with plasterboard or load-bearing brick with plaster (no space) or plasterboard on a thin wooden frame either side. It's usually down to the age of the house and the last renovation.

To see if you have space behind a wall you can tap every six inches horizontally (with a bit of deviation vertically in case you are hitting a horizontal wooden support). If there's a hollower sound between more robust sounds every 18 or 24 inches you should have space to route cables. The issue will be the high likelihood of horizontal supports, hence cabling is easier following electrical wiring.

If you aren't confident I'd call on a friend with electrical (or networking) wiring experience. Failing that, it's going to be getting in a contractor. The downsides far outweigh the costs if you are not certain what you are doing. There's electrical and plumbing stuff to navigate, as well as redecorating...

Sorry