…“dry sex”—going through the motions without actually inserting the penis into the vagina?

Overall, dry sex is a very safe sexual behavior that couples can do together. Whether there’s a risk for pregnancy or disease really depends on how much clothing the people are wearing. If a couple keeps their clothes on, the risk of pregnancy or disease is zero. Sperm, viruses and bacteria can’t get through layers of fabric.

Dry sex or body rubbing with no clothes on can be trickier. If a guy ejaculates on the vaginal opening, sperm can swim into her reproductive system and fertilize an egg if she recently ovulated. Also, some infections, such as herpes and HPV, can spread through skin-to-skin contact, even if the penis isn’t inserted into the vagina.

If both or one of the people has underwear on, the fabric can be pushed out of the way during dry sex, which increases the possibility of risk of pregnancy and/or sexually transmitted diseases (STDs).

So, the more clothing means the lower the risk.

… giving oral sex to a guy?

This is not possible. In order for pregnancy to happen, semen has to get inside the vagina. From there, the sperm that are in the semen swim up through the cervix and uterus into the fallopian tubes. If someone swallows semen, the semen goes through a totally different body system (digestive). Because the reproductive system is separate from the digestive system, there is absolutely no way for pregnancy to happen through oral sex.

However, it is possible to get a sexually transmitted disease (STD) by giving or receiving oral sex (regardless of a person’s sex), including oral herpes. If you and your partner plan to have oral sex, the safest way is to use latex barriers, which even come in flavored varieties. It’s also a really good idea for you and your partner to get tested for STDs before having oral, anal or vaginal sex.

...semen on a hand touches a girl’s vaginal opening, or is inserted into it?

If someone has semen on their hand and then touches the vaginal opening, it is possible for her to get pregnant, though not very likely. The risk is very low. To potentially cause a pregnancy, the semen would still need to be wet on the hand because that is the only way sperm stay alive. Sperm also cannot live long outside of the body.

The best way to prevent pregnancy is to wash your hands or even wipe them off so that your hands are dry. This way, pregnancy isn’t possible.