In order to ensure that submitted and published articles are free from plagiarism, editors will use Turnitin's web-based software to check the similarity index with a quality standard of 25-30%. This process is carried out when the author submits the article for the first time (submission) and the second or next time (revision/after being revised based on reviewer input).
If the article meets the standards, the article can be processed to the next stage (review or publish). Otherwise, the author will be asked to correct it.
Apart from using Turnitin, the editor will also check with Google Scholar and other means. This step is intended to ensure that articles are neither the result of plagiarism nor are already sent/published to other journals (double submission).