You need to temp when you first wake up in the morning. Like before you get out of bed or do anything (you don't want a lot of movement as it can alter the temp). Some people keep their thermometer underneath their pillow. I kept mine on the headboard as mine would end up on the floor, underneath the bed if I did lol
You have to temp at the same time every day. So you'll have to pick a time that you can do every day. This includes the weekends / days off (set alarm and then go back to sleep). A little bit in either direction are fine, but you want to be as close to the same time as possible. My usual temping time was 5:45. Some mornings I had to be up a little earlier, so those mornings I temped at 5:35 which was only 1 or 2 days a week (same days each week).
It sounds like a pain, but it usually becomes second nature pretty quickly. There would be nights that I'd wake up at 2 am and would just automatically grab my thermometer and temp. When I'd go to put it in my chart, I'd realize what time it was and would just go back to sleep.
For accuracy purposes, you need at least 3 hours of consecutive sleep, but 5 hours is ideal. You can still temp if you've had less, but it just won't be as accurate.
You can temp either orally or vaginally. Vaginally, I believe, is most accurate, but most temp orally. Some switch to vaginal if they find their oral temps to be too erratic.
Some things that can alter the accuracy of your results: temping at different times, not getting enough sleep, drinking the night before (though this can vary person to person), and some other sleeping conditions, etc.
It sounds like a lot, but I think I adjusted to temping pretty quickly. It wasn't my favorite thing to be doing, but I feel like it was very helpful in gaining an idea of my cycle.