So I'm reading a book about linux to try and learn more about it. I got to a section bout run levels but it didn't relly explain what they do/are. it just seemed like it ws just for when you wanted that process to run. what happens if you change the run levels? The book explained it poorly and I would appreciate some clarification.

run levels are (at least from my interpretation), simply put, ways of configuring what services are running on the machine, usually the higher the 'runlevel' the more that is configured to run, different distributions handle them differently, but most if not all have runlevel 0 as shutdown, runlevel 6 as reboot and 1/6 as single user mode (only a single root shell and perhaps bare minimum graphics drivers) everything in between is up to the distribution, but they can be customized using runlevel editors so you could have one run a webserver, one a desktop etc..
sorry to seem confusing, but run-levels can be confusing

that makes a little more sense I guess. the run levels are kind of like a precedence setter. it's kind of like "this service is more important that that service" thus the higher run level? Do the run levels boot up in order?

no, they don't, they are more of a preconfigured set of services that run when invoked, you COULD arbitrarily set anything to run in any runlevel, though as i mentioned, different distributions have their own default sets services on each runlevel, but you could have say runlevel 2 have a webserver and runlevel 3 have your desktop, etc..

ok. got that. now I think my book mentioned they boot consecutively, is this true? or does it differ between distros?

they do not boot consecutively otherwise your system wouldn't boot at all since runlevel 0 is halt as a standard for all distributions, if they were booted consecutively the first runlevel that would be reached would be to halt the system, you chose the runlevel that is booted, often times in /etc/inittab, but some distributions have different ways of setting this.

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Oh, ok. thanks for clearing that up.