will I look crazy with just the bar? Or do people do that?
To most people in a commercial gym? Sure. They're all hopping up and down on bosu balls or whatever they like to do. To people who actually know what they're doing? No. Not at all.
Speaking of bench presses should I use the bar for those too? Because I've been using dumbells for that and bent over rows.
Ideally, yeah, if you can be careful about the benching. With just the bar, though, I'm quite certain that if you get stuck you can simply tip it off and stand up, if not easily roll it down your chest and sit up. I sometimes do this with over 200 lbs, so I can't see you struggling much with the bar. You don't have to worry about plates coming off or making a big racket or anything. Generally, if you do fail to get it up, you can still make it to the lower rack on the bench, then get up and pull it back into position.
Also what is ladder training?
Just a training principle the application of which is to allow a beginner to handle more volume than they might otherwise be able to; the basic idea behind which is that as a newbie most of your gains are mental rather than physical, and as such you will be best served by simply getting as much practice as you can. This is particularly true when using heavier weights (in a lower rep range, say 3-5 rep max).
So, say you start benching that 45 lb bar.
Instead of just doing as much as you can (saving absolute failure for the last set, btw), you would do something like this:
45x1, rest a few seconds, 45x2, rest a few seconds, 45x3, rest a few seconds, etc. until you can no longer add a rep on your previous set.
An example 3 sets (the 45 being lbs, the weight of the bar and x# being the number of reps performed, each line break being a new set) of that might look like:
BB Bench Press
45x1, 45x2, 45x3, 45x4, 45x5, 45x4
45x1, 45x2, 45x3, 45x4, 45x4,
45x1, 45x2, 45x3, 45x2
As you can see, each set ends when you are no longer able to "climb a rung of the ladder". In this way you are theoretically performing a total of 40 reps where you might otherwise have only been able to do something like 24 (45x10, 45x8, 45x6 for example).