I would like to know the meaning of "we should not roam about in the hot sun".
Among its meanings, about, as an adverb (NB: It's also a preposition), has the following ones (NOAD):
- used to indicate movement in an area;
- used to express location in a particular place.
Or the OALD that says "nearly; very close to".
EDIT: But as Martha correctly pointed out, here we have a different meaning.