To insert a pause you can use SSML (
http://www.cepstral.com/cgi-bin/support?page=ssml). Specifically insert the following SSML code in your text:
1. Inserting silence / pauses:
"This is not <break strength='none' /> a pause."
"This is a <break strength='x-weak' /> phrase break."
"This is a <break strength='weak' /> phrase break."
"This is a <break strength='medium' /> sentence break."
"This is a <break strength='strong' /> paragraph break."
"This is a <break strength='x-strong' /> paragraph break."
"This is a <break time='3s' /> three second pause."
"This is a <break time='4500ms' /> 4.5 second pause."
"This is a <break /> sentence break."
For pausing while a voice is speaking, here is one possibility:
Use Tex-Edit Plus (this assumes you have a Mac). While the voice is speaking press
[ctrl]+[command]+[, (comma)] to pause. Press the same combination to resume.