Answer 1

well it depends there are companies which could hire you even if u dont have any certificate. but still it's better if u have school certificates along with other ones. chances are that they might want to see it.

Answer 2

Well, they usually check your cover letter and CV, you should put some projects you worked on as a bonus. And if they think you are a viable candidate, they will send you an assignment, mini project, to work on. If the company is satisfied with your work, you are hired.
At least that's the common practice here, in Serbia.
In general, know how trumps any piece of paper, so learn and improve. 😀