I am a bit baffled by your complaints about the Seashore Guide
(help), as from my experiences, it is one of the best help documents I
have read.
I have a feeling this may however be a misunderstanding about
seashore's role.
Seashore is a standalone image editing application, not a plugin for
iPhoto.
With that in mind, you open images for editing as in any application:
File -> Open...
From there, you can go on to add a layer and put in text, etc.
If your guide is the same version as the one I'm looking at, then the
instructions for the text tool is on page 24 (25) -- as it says in the
contents of said document?
To edit your photo from iPhoto, you can set an 'Open with external
editor...' un preferences -- make it Seashore and then Seashore will
Run and open the photo when you click on the external editor option in
iPhoto (i don't have iPhoto on this machine, so I can't tell you where
that might be. I think it's in the right-click menu on photos at
least...)
My eg. workflow fro your task:
open your photo in seashore
add a new layer (CMD+SHIFT+N)
click on text tool (T in the tool box)
adjust the font accordingly (button in the options tab of the options
box -- if you can't see any of these boxes, press 1)
click on the image, write in your text in the box provided, click ok.
condense the layer to the text (Layer -> Extras -> Consdense To
Content CMD+SHIFT+E i think it was).
click the greyed-out links for the two layers in the layers box to
link them together.
next, select the photo layer (probably called background) so it isn't
the one that moves when...
...you align the text layer where you want it using the Layer ->
Alignment options
if you want a bit more space between the text and the edges, i'd use
the Layer -> Layer Boundaries... to add a little space after to
Condense To Content command
Hope that helps! :)
Josh