Some doubts

Hello,
I have being having some troubles with my oneplus one. Today I recieved a notification saying that a new update was available so i downloaded and tried to install. However I didn't realised that i had installed the twrp so i was unable. As i wanted the official update I installed a stock recovery and try to install the update, but it failed. Don't know why it failed... i assume that maybe i didn't installed the appropiate stock recovery. However i finally installed the update by using the "apply update (option in the recovery)" to the official zip file i had previosly downloaded. My question is, for the next update will i have to flash it or just a normal OTA update? (i think that my problem was that the stock recovery was not the appropiate, so I just wanted to know if my recovery has been updated to the appropiate one with the manual update)

Another thing what does the lcd density option does?

Thanks, sorry for my bad english if you don't understand please ask me