Chill chex.
Please explain what you mean by Canon? Ive only read a few starwars comics, I dont know a lot about it.
Ok so up until last year, all the Dark Horse comics(and everything else from the Expanded Universe) was canon. Meaning it was part of the official story and they were part of what actually happened in the tale of Star Wars.
Last year Disney retconned almost everything besides the movies and TV show so everything else released wasn't part of the official story. This is so they could make room for their new movies, comics, books etc. and would be tied down by pre-existing lore.
This might sound confusing so I will just give you
this. That link will show you all Canon things in the Star Wars universe.
You might want to start your collection with the new, canon comic books, including Star Wars, Darth Vader, Princess Leia, and soon Lando comics.