255.02 is the built-in 1 second timer pulse. (ON one second, OFF one second)
You could either program two T4 timers to toggle every 1 second, or if the time is not critical, use a built in S2 Free-Running Clock bit in the identical manner as 255.05 to get 0.64 or 1.28 seconds.
200.01 is being used as the output coil after a one-shot (OSR or ONS). DIFU is DiferentiateUp, or OneShotRising.
In rung 5, the extra vertical indicates the bit is derived from a DIFU instruction. Were it on the right side of the contact, it would be from a DIFDown.
The KEEP instruction for bit 200.00 is identical to a SET/RESET latch. The upper branch Sets the bit, the lower RESets it.
200 is a word of 16 bits. Just as you may pick B3:1 for some group of related bits; the original programmer picked 200 for his/hers. Likely because it's a nice round number, nothing more. Omron does not have dedicated memory areas for Words and Bits, they are from the same pool of CIO memory. They are referred to as channels.
You have inputs in channels (words) 0 and 1, and outputs in channels 10 and 11.
I myself try to avoid the lower words, 100 to 199, as these are the areas where real IO is mapped on some PC models. That way my programs can be ported among Omron models with no change (except where the outputs _are_ in the 100 area instead of the 10 area.)
And before you ask, the TIM004, etc. contacts, are equivalent to A-B T4:x.DN bits. And note that Omron timer presets are in tenths (0.10) seconds, whereas A-B are in seconds or jiffies. (yes, a jiffy is a unit of time - look it up!)
RT