Y axis? Math is hard... is that the one that goes up and down or across
Up/down is current mA draw.
Across is time
So you get a reading of the current mA draw at the sample rate, graphed over time.
Now: is the current draw in mA
Avg: is the average mA over the entire sample set
I believe it also gives you the total mAh for the sample set - ie, if you ran it for an hour and averaged 130mA for the hour, the total hit on your battery is 130mAh... so subtract that off the 1350mAh and see you've used ~10% of the battery.
Stuff running in the background is any app that is running. Today items run, even when the today screen isn't showing - they should only wake up and see that Desktop isn't the top window, then go back to sleep. Other apps, for example tmail (Outlook mail) may be running all the time even if not visible in the "running apps" list, but are visible in a process listing, might be running even when in the background doing stuff (checking email, pulling weather data, rss feeds, who knows
) as long as the device is not on standby (ie, when you hit the power button or it times out and goes to standby on its own) - apps that have requested to be run at a specific time can wake up the machine out of standby... do some work, and then let it time out again.
All that works against your battery life, but the three deadly battery killers remain
* Voice call
* Data use
* Backlight
Along with the forth horseman of the battery apocalypse, WIFI.