Basically installing this gives you an extra button labelled "Alternate" next to the Resources button in the top right corner. When you hover over it it will keep the panel displayed while the mouse is over any part of the panel, or if you click it it will be toggled on.

It displays a list of all the resources that are present on your vessel with a bar graph of the amount on vessel and the amount remaining. It also has the following additional capabilities:

Displays stage amount/usage - so you can see how much fuel is left in your current stage, esp in an asparagus configuration
Adjust the order and Grouping of the Resources so they display how you like - some can even be set to only show up when a threshold is passed
Optionally displays the change rate (or instant consumption) values
Optionally displays time till empty/full (*New in 2.2.0.0)
Optionally hide a resource on empty (*New in 2.1.0.0) or on Full (*New in 2.2.0.0)
Select Resources to see part windows and look at individual components
Transfer Resources between parts - like the standard part windows (*New in 2.1.0.0)
Add Alarms to get visual and Audio queues for what needs attention - even add your own sounds
Maintains settings and visibility between vessel switches/restarts
KAC style update checker added
Movable and lockable panel
Option of the KSP or Unity styles
Ability to add icons by simply placing files in the right folder
Ability for Modders to provide icons with their mod and have them display in KSPARP
Ability to configure the order of preference for icon sets
Optional Staging facility with Ability to Activate Stages in Map View, and
Ability to use Space Bar in Map view to activate stages - like in standard flight mode
Autostaging Controller to activate stages on engine flameout (*New in 2.1.0.0)
Now contains icons for resources from: Kethane, Deadly Reentry, Extra Planetary Launchpads, KSP Interstellar, Life Support By Bobcat, MFS, Near Future, TAC Life Support
API for information reading and alarm acknowledgement (*New in 2.1.0.0)

I plan to add a few more items to this over time, but that's it for starters

Heres some vision of the ARP in use - updated for 2.1

Alternate Resource Panel