The most accurate way to figure out your activity points is by wearing a heart rate monitor. 100 calories = 1 AP. Each point you eat is roughly 50 calories (depends on fat and fiber) so if you eat your APs you still have a calorie deficit.

I find the WW slider thing and the online AP calculator overestimate my APs, so I don't use those. It may be that when I say I'm exercising at high intensity, it's really moderate. So I always had to be conservative when using those tools.

In the old days, WW had rules about using APs, like only eat APs after the first four that you earn, e.g., earn 9, eat 5; earn 4, eat 0. Some people still do that. They also used to only allow you to eat them on the day you earned them, or they'd be lost. Some people still do that also.

You'll have to experiment to see what works for you, but in the long run you definitely can't do a lot of exercise without eating at least some of your APs.