JRT in heat...what to expect?

I adopted a female JRT (2 yrs) and since the shleter did not have any information whether the dog was spayed, the vet reccommended to wait and see if the dog will go in heat and thus prevent an unnecessary surgery if it turns out she was fixed.
I never had a female dog before so I don't know what 'it' looks like? Do they bleed a lot? Does the vulva become enlarged prior to the bleeding? Does the dog become fussy? Nervous?

I assume every dog acts differently, but any infomration common to them all would be appreciated.