If you want to use Bootstrap component, you just need to read the document on http://twitter.github.io/bootstrap
Try to output the markup as Bootstrap required and it will work.
Your question is too general, so it is quite long for me to tell you all cases.
And by default, Joomla seems not provide any "contact" module.
All you need is output the markup which Bootstrap modal required. You can add those markup to article, custom HTML module or enter directly on a file in \templates\temp_name\tpls\blocks folder.
For example, here is the thread about the Bootstrap carousel