Looking at the "Analytics" tab of your Creator Studio can be really overwhelming. As a creator, you need to know what reports you can get the most information from and move on so you can continue creating for your channel, and not scrolling through Excel sheets. Here are the 4 sections you should be checking each month.
The first and most important report you should be looking at is Watch Time. This single metric determines so much of your success on YouTube. Watch Time is the amount of time a viewer spends watching your content - this can be across a single video or even a whole channel. YouTube's algorithm for suggested videos and search results prioritize videos that have higher watch time because higher watch time leads to a longer overall viewing session on the platform. An important thing to note is that Watch Time is not how much of your video was watched, but how much your video contributed to a users' overall content-watching "session" on the platform.
Because Watch Time is so abstract, the next thing you should be monitoring is your Audience Retention. The higher your percentage viewed usually lends itself to higher Watch Time, but that is definitely not the rule. Audience Retention gives you an idea of the watch time you are creating for viewers on your channel. As a rule of thumb, longer videos (6 minutes+) with percentages viewed over 50% lead to higher Watch Time. A shorter video (less than 3 minutes) would need over 80% percentage viewed and much more views to match the watch time of the longer video.
As a creator, another section you may find really interesting is Traffic Sources. In this view, you should choose one of your more successful videos in the search bar, and view the sources of views (and watch time) for that video. You may be surprised to find that a lot of the traffic came from being one of YouTube's "Suggested Videos" or perhaps it was from a certain playlist. The analytics go much deeper than this first screen, though. Next, click "YouTube Search" in the list of Traffic Sources. This will bring you to a screen where you can see what people searched in YouTube to find your video. This gives you a lot of valuable information: common misspellings of your channel name, another video they could have been trying to find, or abbreviations you didn't know fans used. You can use this information to better tag and title your videos in the future. Return to the list of Traffic Sources and click "External". This will show you what views you received from external sites like Google Search, Facebook, Twitter, or possibly a blog/website that did a feature on the video. This can show you just how fruitful a premiere was for a particular video and help you determine if you would want to do that again.
The last metric you should look at is your Subscriber Rate over a period of time. Set the parameter to "Last 28 Days" so that you can actually hover over specific points on the graph. Look for spikes and drops, and compare the days of those spikes and drops to your release schedule. What did you release on those days that either really got people excited or turned them away? Use this information to inform your content calendar going forward. If you continue to lose subscribers or gain less than normal, then you should consider not continuing with a certain series idea on your channel. Additionally, you can set a "Compare Metric" as "Subscribers Lost". The blue line shows the subscribers you gained over the last 28 days on any given day, and the orange line shows the ones you lost on the same days in that time period. If at any point the number of subscribers lost is higher than the subscribers gained that day, it is very important to pay attention to what happened on your channel that day.
There are many more reports to discover in Analytics, but at the very least you should start with Watch Time, Audience Retention, Traffic Sources, and Subscribers. Once you familiarize yourself with these, you will be more comfortable with looking into other reports and interpreting them.