I read the other post on subscripts. I am looking direction on how to use a single subscript for use in an array.

See mathcad "Seeded Iteration" example here:
http://www.imakenews.com/ptcexpress/e_article000950717.cfm?x=bbPFVpp

Per another posting, I also realize that units are not built in ... yet

As a request, now that SMath can read mathcad files, can we save to mathcad files?

Also, what are the short cut keys that you have programmed in? I love the fact that this is so much like Mathcad!

Hi. Single subscript, Units, Mathcad files saving would be added in future versions.
Here is the complete list of shortcuts:
Ctrl+Z - Undo changes
Ctrl+Y - Redo changes
Ctrl+X - Cut
Ctrl+C - Copy
Ctrl+V - Paste
Ctrl+M - Insert Matrix
Ctrl+E - Insert Function
Ctrl+T - Insert blank Image
Ctrl+. - Symbolic calculation of the equation
Ctrl+Shift+P - Insert PI constant (3.1415...)
\ - Insert square root
Ctrl+\ - Insert n-th root
[ - Insert el() function - subscript

Find actual shortcuts on Built-in Shortcuts post.