Studying A-level as a international private candidate, need some advise.

Hello guys, I quit my IB school about a year ago when I was halfway done with my second year in high school. I'm considering studying A-level as a private candidate and I have a few questions about it.

Do I need to study any other things (besides the exam)to get the certificate of A-level?
Would it work to study English language, Psychology, and Economics?

All I want is a certificate because I want to learn carpentry in Canada and seems like there isn't any requirement but completion of secondary school.
Please give me your advice, thank you! :3

First, establish what exam board(s) you're going to be using. Read the specification for those subjects with that/those exam board(s) and check that all marks come from examinations - i.e. there there is no coursework or "non-exam assessment" component. If there is, it makes thing trickier as a private candidate. If you were doing one of the main science subjects, I'd also say to look out for the "practical endorsement", which can be problematic for private candidates.

Once you've done that you, need to register with the exam board(s) as a private candidate and then find somewhere to actually sit your exams. You can find a search too to do that here.

Quick question. If "there isn't any requirement but completion of secondary school", then why take A level at all? In the UK secondary education ends with GCSEs. A levels are classes as further education. Do they define secondary education differently in Canada?