[confused word user]

Hi. I use Word 2003 at work, and if I decide I want to, say, enbolden
some text, I highlight it, either use Control=B or click on the bold
button, but then all the text in the document is enboldened - happens
whatever formatting I'm trying - italics, changes of justification,
etc.etc. I can undo all but the section I want by using Control+Z,
but it is VERY annoying. Does anyone know how I can stop this
happening? Thanks.