I am suprised it has not been mentioned to only use the official site otherwise you will be scammed into paying up to £80.00.
The site is:- https://www.evisa.gov.tr/en/
Also, although I don't need to use it as I am a resident, I believe there is a question on there and people often look for the answer 'Turkey', but this is not what they are asking for, as it is a Turkish Visa you are applying for!!
The answer is about you, so British or UK Citizen is the answer!!
Sorry, might have this bit slightly wrong, but hope you get the gist of what I am saying when you apply.
2nd part 1st,
Yes at the beginning it asks what country, rather poorly worded but as you know it is asking 'From which country are you applying'
1st part, TBH there are some things we/I get fed up with which is people jumping in (no one so far on this thread) asking questions before even doing the smallest of searches, which and where using the official site has been mentioned on many occasions along with some of the rip-off fees other sites may charge, obviously a expensive lesson but may encourage people to try searching first, then come back as I think the OP has done to confirm what he/she thinks.
Or to put it another way, it's not always humanly possible to remember, recall and suggest everything that should be noted, so sometimes thing slide on by and maybe go unmentioned. (but not for long in this case)