Initial onboarding to all the teams is provided by Ilmari Lauhakangas. You can schedule an interview with him via email: ilmari.lauhakangaslibreoffice.org
Once you decide what area of the project you are interested in contributing to and explore the information available on this wiki, you can introduce yourself on our main mailing list libreoffice. Normally you will get a response quickly with an offer to help you.
We use #libreoffice-dev for online fast communication, this is especially useful if you are stuck with a problem and would like quick advice.
Please see Find the expert for a list of people to contact with specific problems.