Hi there wswx, and welcome to Scarleteen!
All of these are great questions to be asking! I'm glad that you're thinking about how to take care of yourself and your partner before taking any steps that might incur any risk of contracting an STI.
I'm not entirely sure what you mean when you ask what leads to "complications".. complications that occur after having gotten the vaccine and being exposed to HPV? Complications as a result of getting the vaccine?
As for how the vaccination works, you can read all about it at The STI Files: Human Papillomavirus (HPV)
. The gist of it is that there are over 100 different strains (types) of HPV, but there are only a few of them that have a high risk of causing things like genital warts and cervical cancer. The vaccine protects against 2 types of HPV, 4 types of HPV, or 9 types of HPV depending on which brand of vaccine you go with. The vaccine is most effective when administered before someone has become sexually active, because then it's very very unlikely that they've been exposed to any strains, and will gain immunity from whichever strains they are vaccinated for.
To answer your question about your partner, if they haven't had any sexual contact
with others, having sexual contact with them for the first time should not be a risk. However, HPV is trickier than the other STIs in that it's not only spread through contact with sexual fluids and/or intercourse, but also from skin-to-skin contact (a.k.a. even if someone who has HPV doesn't ejaculate, if your genitals touch they could possibly expose you to it). So hypothetically if you were with a partner who had never had intercourse, but had exposed their mouth/anus/genitals to someone else's mouth/anus/genitals, they could be at risk for contracting/transmitting HPV. Then, it would be important to use barriers like condoms and/or dental dams to protect against HPV as well as other STIs.
In terms of what to do while getting the vaccine series, if you and your partner haven't had any sexual contact before, and do not have sexual contact with anyone but each other, then you shouldn't be introducing any risk of HPV or other STIs when you have sex, and it shouldn't affect the effectiveness of your vaccination at all.
While we're on the topic, is the risk of pregnancy something that might be present in having sex for the first time? If so, have you thought at all about what you might do to address it?