What kind of proof do I need to show that im a Plumber or welder in Canada?

I want to immigrate to Canada LEGALLY but my Nicaraguan degree "Software engineering" is inferior plus is not in demand in Canada, a couple of the on demand skills are plumbing and welding, And I think im going to learn to do these things.

I just want to know how would the Canadian officials know that im a welder or plumber because at least here in Nicaragua there isnt a university degree for that... I mean im sure they are some sort of true but how would they know thats my question, do I need to pass some sort of test... PLEAASE inform me!