You can add directories to the path by editing your s:user-startup file.
For example I'm obsessed with keeping my C directory as clean as possible, so I have all my external binaries in sys:bin. Thus I have the following in my user-startup:
path sys:bin ADD
Remember the add in the end, else it'll change your path to point only to sys:bin, and we don't want that. :-)
I'm wondering, is there an AmigaOS tutorial on the net? I've personally learned by reading the manuals whenever I bought an OS update back in the day, but nowadays many people getting into Amigas will probably never see an AmigaOS manual live. :-/