Firstly after downloading recount, make sure that it is enabled in game.
You should be able to see the box as circled in red below.


Go to the paper-icon and click it, and tick current fight, this is the case for most people, I don't see how anyone would be using other options. It measures the DPS for a period of aggro-start till aggro end.



In order to report your DPS results to guild, raid, party or whatever, just click on the horn button, and tick wherever you want to report it to, and it will post your results.



In event that your recount crashes or just froze, and will not record any data in any fights, simply make a macro as shown below and click it a few times. It will be back to work as normal.


Macro code below.
/run local f = CreateFrame("frame",nil, UIParent); f:SetScript("OnUpdate",CombatLogClearEntries);

Thanks for reading!