send information from Excel to an outside program

I am trying to send information FROM Excel to an outside program. I was hoping that I could make it so that when I use the SendKeys that the code can read what is in a cell on the Excel Worksheet
Example
Cell B4=Username
Cell C4=Password

In my sendkeys I want to reference what is in these two cells, but without typing in the text so that it can be changed with each user.

Is there a way to reference cells with sendkeys???
Do I have to select the worksheet and cell???

Please help

Thanks in advance
Chrysti