Where to start? LibreOffice source code

My first time here. I downloaded source code, but I don’t know where to start. I don’t know which file to look first, I know basics programming knowledge. So I want to look at source code to learn something new. I checked the map of source code, and looked the files on the top, but it is still confusing.
is there a beginning of everything?

You can start from this page https://www.libreoffice.org/community/developers/. It contains a few useful links, especially Learn more about code and development. Look at easy hacks to see some tasks for beginners. Login to IRC and subscribe to the mailing list to talk to developers. When you understand how LibreOffice code is organized, You can move to a more complex things like fixing bugs.