Statistics explanation

I’ve looked all over the website and can’t find an explanation of my learning statistics. (If I just haven’t found it, please tell me where this information is located.) I understand the actual statistics for new words learned, lessons, etc. which I can adjust for today, yesterday, etc. but what are the numbers to the right of these? At first I thought this was an average of my past achievements but the numbers no longer make sense to me. Plus, on another page, there are numbers with plus and minus signs in front of them. What are they related to? That is, I supposedly did something +5 from what?

If you mean the numbers all the way to the right, those are your goals, which are set by the level of LingQ you are at. (Beginnner 1, 2, Intermediate 1, 2, etc)

Does that mean that the numbers at the right remain constant while I stay at a particular level? Are these goals for each level described somewhere on LingQ so I can see what they are before I reach I particular level? Moreover, do they vary with the language being studied?

The progress snapshot displays your progress over specific durations of time. There are targets set (that show on the right hand side) and the bar shows how close you are to achieving that target.
Targets will change with each level you reach. There are some small differences in numbers for a few group of languages, but for now on the site you can only see how many known words you need to reach different levels, on the avatar help page: Avatar Help