Fetal Doppler

Celine
Hi ladies I got my Doppler today and apparently I do now know how to use it so I need some tips on how to find the baby's heart rate!! I found it to be around 120-130 in thinking that's inaccurate,  but then I found one to be 177 and 193.  Also what does the button on the left mean? It has 3 lines and you're able to change it from 1, 2, 3? 
Thanks!