The Event Viewer logs everything. An error in the log isn't necessarily a problem in itself; you can drive yourself nuts trying to track down every single entry, but it won't noticeably improve your computing experience unless you've noticed a real problem outside of the log.
There are, in other words, a lot of practically harmless errors in your log. I heartily recommend you don't try to chase them all down unless you have a real and demonstrable problem that occurs at the same time as a given error or set of errors in your log.
That said, the best way to fix the errors (if you're inclined to do so) is to google the error codes/messages. That's the best answer I can give you based on the information you've provided. If there's a particular error with which you'd like assistance, feel free to post the relevant info and we'll do what we can.