Don't want to sound stupid...

I am ttc baby #2. My daught is almost 2 and she was the best "oops" we ever had. I didnt know i was pregnant til 12 weeks. I still had my period on time for those 3 months. Well we have been trying for 6 months now for #2 and I have know idea what i am doing. I see some postings saying "10 dpo" , are you going off the last day of fertility on your calendar here or are you testing the exact day to know what day you ovulated?