I am kind of new to this, I use SAConf to change my rules, so how do I run spamassassin -tD
That's a command line program, not a configuration option. It's a way of actually starting spamassassin from the command line with the "test mode" and "debug output" flags enabled. However, you need to be at a command line to do it.
ie: spamassassin -tD <message.txt
Actually, if you've just been editing, first thing you should do is lint your rules.. it helps pick out the simple typos. Lint mode should run quietly and exit. If it prints anything, it's complaining about a config line it does not understand.
spamassassin --lint