modern shopping carts (even zen cart!) are quite complex. the idea that you are no php expert and that you are frustrated is not surprising.
zen-cart does NOT make use of java. it does make use of javascript. they are very different.
some javascript library saying Opera or MS Edge or any other browser is not supported, is again not surprising. i can guarantee that ZC will work with those browsers.
without looking at your specific installation, it is hard to say exactly what is wrong. you think the log files are not helpful, but did you not say you are not a php expert? log files are one of the crucial items that are helpful to a seasoned php developer.
finally, do you honestly think that the default template for checkout shipping is wrong? forgetting that you are a self proclaimed no php expert, zc 2.1.0 was released over 2 months ago, and from a logic POV, do you think you would be the first person to find a rudimentory error of this sort?
if one were to look at
this single line of code, that php function will draw the opening form tag for said page.
my advice is to hire a seasoned developer or start posting log files of errors that are getting created or screenshots of errors in the developer tools console. perhaps then someone could help with your problems, and in the process you might learn a bit more about php and how ZC really works.
best.