After (and sometimes even before) a seller accepts a buyer's offer, the buyer will have the home inspected.  Home inspections are done by licensed inspectors.  When I'm represeting a buyer, I can recommend the very best in town, and typically coordinate their schedules with the buyer's and mine to make an appointment for the inspection.  Inspections typically run about 2.5 hours +/- for a house and more like 1-1.5 hours for a condo.  The inspector will prepare a written report but if they're available, it's good for buyers to be present during the inspection so the inspector can point out and explain things in person in more detail.  It's also an opportunity for a buyer to spend more time in the home they're soon going to live in.

Inspections generally run $450-$500, more than that for larger homes or multifamily properties and sometimes less than that for smaller homes and condos.  The buyer pays the inspector at the time of the inspection.

Avoid unpleasant surprises later on.  The main reason for a home inspection is to identify major defects that would be significantly difficult or expensive to get fixed.  Buyers need to be aware of those defects and make an informed decision to assume responsibility for those repairs after closing, ask the seller to make those repairs (or credit the buyer money to do so) before closing, or disapprove the inspection and terminate the transaction.

Beyond that, the inspector will identify any minor defects the buyer should also be aware of.  These might also be negotiated with the seller.  The inspector may also give the buyer recommendations for long term maintenance of the home.

Don't sellers have to disclose everything?  Sellers are responsible for disclosing any known defects to a buyer through the seller's disclosure statement.  But many homeowners may not be aware of 100% of the issues an inspector might note - especially if they don't spend a lot of time in their crawlspaces, attics and other tucked-away places where leaks, saftey hazards and needed repairs can easily go unnoticed until a significant problem occurs.

Well, duh!  Much of the condition of a property is readily apparent and should be taken into account in a buyer's offer to purchase the property.  As an example, if the hot water heater has rust all over it and is dripping on the basement floor, it's pretty obvious it's going to need replaced.  If the carpets are worn, stained and dirty buyers shouldn't expect a seller to replace them based on an inspection - that was obvious at the time the buyer made the offer.  

I encourage sellers to disclose, disclose, disclose! and try to make sure buyers are aware of likely defects in advance of making an offer to minimize suprises and occassionally difficult, stressful negotiations later on.  But there are often issues that an inspector may identify that are a surprise to both the buyers and sellers, like things in crawlspaces or attics that buyer's don't look at beforehand and sellers may not be aware of.  Sellers are often willing to address or help address significant structural, functional and safety issues they may not have been aware of prior to an inspection.