The output of the Trace Logger depends on the system you're on, as different systems have different CPUs with different assembly languages. To make sense of what the Trace Logger puts out, you need to know the ISA of the CPU you're working with and understand ASM in general.
On the example of NES, here's your average Trace Logger line and what it means.
C5C3 8D STA $2007 A:00 X:04 Y:E1 P:B5 SP:FD Cy:212836 NTBIC
C5C3: The location of the instruction that is currently being executed.
8D: The opcode, in this case (STA, absolute).
STA $2007: The current instruction.
A:00 X:04 Y:E1 P:B5 SP:FD: The current state of the NES CPU registers in Hex BEFORE the instruction was executed.
Cy: The total amount of CPU clock cycles that have passed so far.
NTBIC: The NES CPU flags that are set before the instruction was executed.
On Bizhawk, different cores put different things in the trace logger, depending on the system. Some of the above applies to other cores, some of it doesn't. To get more specific help, post the system you're using and if there's any specific section about it that's giving you trouble.
