First time ttc

A little background info, I conceived my son while on bc pills and didn't know until I was 8 weeks pregnant. I am off my bc pills starting today so we can try to concieve #2. I have a few books I'm reading on ttc and what to expect before (my son was born at 27 weeks so I'm trying to take in as much as I can to get the whole experience this time).

Anyway, I was hoping to get some quick questions answered that I had while reading.

Cycle day 1- is that the day you get your period?

Basal body temp - is that just a normal thermometer? If not where can I get one?

-Is it taken at the same time everyday before getting up?

Opks-what is the cliff notes version of how to use these?

I swear I tried Google but a lot of these things completely went over my head. I am 29 years old, will have a high risk pregnancy and will deliver by classical c section by 37 weeks no matter what so I may be a little scatter brained. Please any help would be appreciated.

Thanks!