When you have the weapon card open, there’s an option to View the weapon; you can then zoom in/out and rotate it to get a good look. @Adabiviak already gave you a link to the parts posters, but you can find additional information in the various parts guides. Some of the other things you might want in a weapon you can tell by the name - you’ll find that covered in the same post.
In terms of getting the gear, if you’re still levelling up your character it’s not such a big deal getting exactly the right parts, since you’ll out-level it sooner or later anyway. If you’re at maximum level and looking at end-game activities, then it pays to give more attention to these things especially if you’re trying to maximise your gear and build for dealing with raids.