Power over time for RC ish circuit in LT spice
There are two methods already mentioned for you in:

How to integrate a signal in LTSpice?

You really should start out with a search here. Spehro provides one method there, using a behavioral source ('bv' in the F2 dialog box) that you add to the schematic. Then you can probe that using the plot display viewer, use cursors to get values, etc. Another way was ALSO provided by Sergei on that same link. This uses .MEAS (just hit 'S' on your schematic and get the pop-up that allows you to create one of these) to perform the calculations for you. You can then use the View/SPICE Error Log menu choice to cause the error log to popup and display your measured value there. It's a great way to go if you know the exact start and stop times, for example.



Technically, I should have just commented all of the above to you. But it is long text and would have taken several comments to achieve. But also, I'm willing to post up an example case if you modify your question to be very specific about an example you'd like to see and don't feel you can work out. So I've added this as an answer with that in mind, as well. Just in case.