[OS X TeX] Writing an Underscore in LateX

[Ishe Chinyoka]

Hi,

I am having problems trying to write underscores in my document. When I write something like "Introduction_to_computers", and try to typeset this in TexShop, from the log it appears as if I missed out something. What on earth can I do to write underscores? I am not in Maths Mode and I am just writing a prose document. 

Thanks everybody for help,

Ishe