We can see today hamza and na-nach people wearing amulets etc. but what is the true understanding of Judaism on this?

Mainstream Judaism doesn't use them and generally views their use negatively. We do find mention of amulets [="kameyot"] in the Mishna in Shabbat, so apparently some wore kame'ot (amulets) in ancient times, but even there, the Talmud relates to amulets that "haven't proven themselves" (Shabbat 60b), which may very well have been the general feeling among the rabbis. The Rambam speaks negatively against them (Guide for the Perplexed 1, 61), inferring that it's like a placebo for the simple people, and surely not ideal (Hil. Tfilin, 5, 4), and the Shulchan Aruch allows to try and protect oneself with an amulet but not to heal oneself (Yoreh Deah 179, 12). Some Kabbalists and certain Sepharadic Jews do hold from them even today (e.g. the Chamsa) citing the Chida & Ben Ish Chai, but their use is generally not accepted by most in modern times.