What power meter would work on my bike? I have a 2015 bike with a Shimano 105 group set the cranks are 172.5mm and behind the crank is says the following. I’m relatively new to cycling and want a power meter please help cheers
This is a big topic. This is the best place I know of to do research. Fair warning, even "cheap" power meters are expensive, although Sensitivus might be changing that.

There are several places where power can be measured on the bike:


The crankarms (probably most common)
The chainrings
The bottom bracket
The rear hub
The pedals


These all measure power based on the same principle: a strain gauge. Power also can be estimated using gadgets that measure your aerodynamic drag and correlate that to your speed over the road.

With the pedals and crankarms, you can get single-sided or double-sided, one being much cheaper.

Pedals are easy because there aren't really compatibility problems, but you'd better like Look-style pedals—I don't think there are any other pedal systems available with power meters, although Speedplay has been acquired by Wahoo, so that might change.

Crankarm-based systems are pretty straightforward: there are some that are add-ons to the same kind of cranks you're using now, and you can even send your current cranks off to a couple of companies and have them put power meters on them.

Obviously a rear-hub power meter needs to be built into a wheel. Again, that's very straightforward to install (and if you've got multiple bikes that can take the same type of wheel, this is probably the easiest way to move a power meter between bikes).

Bottom-bracket power meters are fairly unusual and bring with them all the compatibility questions that you'd expect from the plethora of BB standards.