Both Handel and Bach wrote for the same types of instruments - small orchestras, solo instruments, harpsichords, pipe organs, vocal soloists and choruses - and both wrote some of the same types of works - such as Suites, Fugues, Partitas, Preludes, and other common items in the Baroque era. So that's a start. As the previous answerer noted, Handel wrote some operas and Bach wrote much more church music instead (especially Cantatas and Passions).
To distinguish the two only from listening is not the simplest thing to do. But there are two general rules I can think of: Handel tended to have simpler harmonic progressions (what pop musicians call "chord changes"), whereas Bach had many more surprising and intricate harmonic shifts; and Handel preferred somewhat simpler textures, with generally only three contrapuntal voices (this means three different melodies happening at the same time, like one in the basses, one in the rest of the strings, and one in the oboe), and Bach was truly incredible in his ability to write music with four, five, or even more contrapuntal voices.
Please understand that this is an oversimplification and not always the case, but I hope this provides you with something of a useful answer.