How to understand WarcraftLogs
For the basis of this example, I'll be using this link: https://www.warcraftlogs.com/reports/HQ9xzR6c4fnaGAX2#fight=15&type=damage-done
This is our best attempt on Mistress as of 9/27/17. For those there last night you may recall we kept everyone alive up until we slipped towards the end in that final phase, but up until there this attempt was top notch. That being said, that's only mechanically. When you open that link, it goes to a page with basically two things, a graph, that we will ignore, and a chart under that that probably looks similar to your recount meter (or whatever damage tracker you use). Now this is focusing entirely on damage done, the number that matters for a DPS class. You'll notice above the graph there is a grey bar that allows you to change what information is displayed be it damage done, damage taken, healing, etc. If you want to look into any of those, this is all the same thing.
Now to breaking down the chart that looks like recount. I'm just going to go by it through the columns and explain them, starting with the "Perf %". This is simply comparing your performance to every other person of your class that has posted a log in the past two weeks (a lot of people). Now don't take this very heavily to heart, we aren't professional raiders. nobody is asking us to be so, you don't need to have those big 80+ parses. You have to keep in mind nearly every raid has someone logging, even the big guys that race to finish mythic as soon as possible. I'd say that so long as you roll around 40-50, or higher, on your % you are doing fine. You can mouse over the individual parse percents for each player listed and it will tell you how many other players its comparing with. In this case if you mouse over Slickrick's parse of 87%, you can see its comparing to over 10,000 other assassination rogues, so its a fairly accurate assessment. The following column is the name column, which doesn't need any explanation. I hope you know your name.
The next two columns are pretty straightforward. The amount is two different figures, the percentage of the raid's damage you did. and then the actual amount you did. Again using Slickrick as a point of reference, you see here he did 15% of our raids damage, totaling 775.30 million damage to the boss. The ilvl column next to this is exactly what it says, its just the item level you had equipped during the fight. Next to this however, is essentially a more accurate Performance % from the first column. This does the same as the first column, but compares your performance to people within two item levels of you, meaning people of the same basic gear level. This is usually the best representation of your actual performance, but there are often a LOT less people to compare to here so make note of that.
Following these columns is the Active one, which is literally just the percentage of time you were alive and fighting during the fight. If you died half way into a fight, your active time would be around 50%. Pretty straight forward. This column is also nice as you can mouse over it to see your DPS while you were alive. If for some reason you died to something outside of your control while doing well, you could check this column to get a more accurate depiction of your DPS on the fight. The final column is your total DPS for the fight. Now again, I will say this 100 times over, DPS is not the end all number to follow. If you pull 4 million DPS for 30 seconds and then die 31 seconds into the fight, you didn't do good. By the time that fight is over that number isn't still 4 million, as it the damage you do over a interval of time. I've been asked to make this very clear. DPS is not what determines if you are playing well. End of the fight, look at damage done. That's where it all matters. To give an example here, take a look at Silvalar, no particular reason other than it looks like he died slightly before the rest of us (this was a good pull nobody did anything wrong here). Notice in the DPS column Silvilar's DPS is listed as 487k, but if you move your mouse over the the Active column and mouse over his percentage of 82.85%, you'll see that while he was active his DPS was more than 100k over that. This is because during that time after he died and the fight kept going, it's still calculating his DPS even though he's not doing damage. So again, keep in mind, DPS is NOT what to judge yourself on.
The last thing I want to point out on this is that you can click your name, or anybody's, and pull up a more detailed damage spread of your damage based on ability. Some people may find this useful so I wanted to mention it. As always, if you have any questions regarding any of this, or need help with something don't hesitate to ask me. If I'm not online send me mail in-game @Shaboigles or feel free to add me on Battle.net as Shaboigles#1770 I'm more than glad to help with anything.