By convention, on-line help for all of the buttons is available by clicking on the button with the right mouse button. The help texts are stored in the database just as any other data.
Additionally, there is much helpful information in the `Help!' window which you should get when you log in and which is available by clicking on the Command Menu `Help Window ...' button. Amongst these are topics such as M-L keyboard commands, Text Editing, The Command Menu buttons, Glossary of xlincks and LINCKS words, and more.