No matter how sharp a knife is at the beginning, after some use it needs sharpening, something that you can achieve with a sharpener, sharpening stone or honing rod.
You can tell if your knife cuts well with an easy test using the knife and a piece of paper. A sharp knife can easily and cleanly cut through a piece of paper. On the other hand, a knife that needs sharpening will struggle and its cutting will be uneven.
It is also advisable to sharpen your knives with a professional occasionally, to repair possible damage to the blade's edge and to maintain sharpness.