You can not get by putting your finger inside your body*.
Other things that you can put inside your body with no risk of pregnancy:
A dildo or vibrator
A fruit or vegetable
Someone else’s finger
In fact, the only things that you can put inside your body that carry a risk of causing pregnancy are a penis that is attached to a fertile man or a semen delivery device such as a turkey baster or syringe (… and those things only if they actually have semen inside them.)
Explanation for why you can’t get pregnant by sticking things other than penises into your vagina:
It’s not the vaginal penetration that gets you pregnant, it’s the biological alchemy of sperm meeting egg. In order for someone to get pregnant, sperm need to be present – usually in the form of ejaculated semen.
*Once again, this was a real question.