Customizing OS X Finder toolbar
Which kind of buttons are you talking about?

If you want to customize your toolbar by adding or removing existing buttons:


Right-click in the Finder toolbar and select Customize Toolbar… from the context menu
Drag the buttons you want in or out, and place them where you want them.
Click Done.


[This also works for most apps, btw.]

If you want to add new buttons that aren't shipped by Apple:


Just drag them into the toolbar.


For example, I've used Refresh Finder for years (Macworld review).