If you know a commandname but want to check the syntax, type the beginning of the commandname, then the tabulation key, this will display the command index, with the current position at the first command after the commandname begin. You have a short description and a few examples displayed. Left-clicking on an example should complete the commandline with this example. Right-clicking will fill up the arguments inputlines with the example, so that you can modify some of these arguments before hitting OK. You can get a more detailled help inside your browser by hitting the Details button (this works for most but not all commands).
If you don’t know a commandname, you might find it using the menus or browsing the table of contents of the CAS manual. If you know the TI89/TI Nspire CAS or the Maple language, you can also try their commandnames.