Rob:
Welcome to the GP community!
In GP, the basic way to alter a form is from within GP itself. Click on TOOLS > CUSTOMIZE, if Modifier or Visual Basic Editor is enabled you are good to go. If so, let me know and I'll give you pointers on how to do the deed there. There is a steep license for 'Modifier', though, not all installations have it.
If you want to buy a modifier license, let me know ($3 -10,000), I'll have someone call you.
Modifier allows you to alter the visual interface, the VB Editor allows you to place code behind the buttons that you add.
Visual Studio Tools for Dynamics GP will allow you to add code behind the buttons that you create with Modifier also... but not to place the actual button on the form. I've waited years for this tool, I'm very excited to have it. VBA is so limiting...
Amending reports (starts to twitch uncontrollably)...
GP's 'Report Writer' is a lamentable tool that allows you to modify stock GP reports. To use it, you print the report to the screen and then click on TOOLS > CUSTOMIZE > REPORT WRITER. I'm not sure if it comes with the basic GP install, I don't use it unless threatened with bodily harm. I prefer to use Crystal reports and stored procedures.