I think from what I know, the women just do it naturally themselves. So where they would normally come from fingering or fucking themselves, you can help them to squirt/cum (squm?) by fingering or fucking them yourself. But the squirting is only their body's natural reaction.
Usually they will tell you as well. Sadly squirting is quite rare but is fun when it happens. I would say there are three types of women:
1. Doesn't squirt
2. Gets VERY wet, you have splashback from the hard fucking
3. Squirts
I'd estimate them at:
1. 85%
2. 10%
3. 5%