LingTree is a relatively simple program. It comes with two resources, both of which are accessed via the Help menu item.
The user documentation is at Help menu item / User Documentation. Please read this (relatively short) document to learn about what LingTree can do. It is also available online at User Documentation.
The second resource is a Quick Reference Guide. This is a summary of what to key in order to get a certain effect in the tree diagram. Use Help menu item / Quick Reference Guide to see it.
Both of these resources will stay showing while you work on a tree diagram (the user documentation is a PDF file). This is an attempt to make them handy for quickly seeing what you need.
Some sample tree files are also available. Click LingTree Samples Zip file to obtain a zip file containing them.
You can also see the LingTree Helper web site for another way to key tree diagrams that some users find more intuitive.