Hope this will help you:https://syntheticgrasswarehouse.com/hiding-your-artificial-grass-seams/
Denis, here is a video that should answer your question!
Denis, you really ought to watch the video suggested by Rose, and the detailed slideshow cited by Redcatcec. These include almost every question you could ask. I have one tiny suggestion: remember that as time passes, the ground may shift. While that can affect the foundation, sidewalk and driveway, it may also affect the lawn, which in turn will affect artificial grass or anything else sitting on the lawn. Don’t expect perfection in your lawn forever. But enjoy it! ☺️
You could use a curved upholstery needle and fishing line and sew them together.