My girl just finished her season. It was her second but my first time having her at home. She went on vacation to my breeders for safe keeping the first time around last fall, as I do have an intact male at home.
Her cycle will last 3-4 weeks. I have been told to keep her safe and away from intact males for a full 30 days after showing signs of being in heat. I even went a step further and only allowed supervised play between my male and her for the fifth week. Mine only bled for 2 1/2 weeks of the 4 week cycle. I didn't use diapers or anything, just regular washing of doggie laundry and I kept blankets out on the couch (I allow mine on my furniture)
Keep an eye on her if she spends time outside as Pat said. Dogs will come from all over to get to her if they can!
You can expect swelling of the vulva (some get very large), bloody discharge and increased urination (territory marking). Afterwards she may experience a false pregnancy, common among 1st seasons, where her nipples may swell up and can produce a little milk and she can develop a little bit of a tummy. This can last a few weeks. Her nipples will probably be bigger after her season and won't be as small as they were before.
My girl becomes a total love, super snuggly/cuddly and slept a lot while she was in season.