we have been in a similar "having no clue situation" last year.
You can look for RYA schools and certification
. They offer various levels of certifications, from a 2-day "Start Yachting" weekend up to a several weeks/months training and certification
of the so called "Yachtmaster".
As far as I can tell, those certificates are globally well accepted when it comes to chartering a boat
for a holiday.
(In fact, many charter
companies I have seen so far, do ask specifically for the "RYA Day Skipper" certificate, or something comparable as minimum before they are willing to give you a boat.)
Depending on what you want, you can start with the Competent Crew or directly plan for the DaySkipper if your holiday is long enough.
RYA education scheme - General Infos/Overview
RYA Day Skipper
RYA Yachtmaster Info
If you are serious about sailing, then this might be what you want.
PS: I have never heard anything that you are required to have a license
from you country of residence. (Would be pretty odd, if you move from one country to another for example.)
The RYA is, as far as I can tell, certainly not bound to your passport and internationally well accepted. - RYA would be my recommendation (regarding proper training as well as in regards to international acceptance).