Yes, IFA is open to the public.
You can even purchase tickets online in advance.
Just have a look here: http://b2c.ifa-berlin.de/Tickets/TicketsEnglish/
But those tickets do not include public transport.

I would recommend to buy an admission ticket including public transportation on the day of your visit (unless you already have a day-/week/-monthly ticket for public transport).
Admission incl. transportation tickets are sold through the BVG ticket vending machines - almost everywhere there is a tram/U-Bahn/S-Bahn station (and even at Tegel airport although it is served by busses only).