To host - Generally I use this word when hosting a party, hosting guests, etc. To hold - this word is most often used when holding an object, for example, holding a bat, holding something in your hands. You might say you are holding a party... but I think I would usually say having a party instead. You can also hold a table - this means the table is reserved. There are many different ways you can use "hold" - so depends on context. I can't think of another scenario where "host" and "hold" could be used interchangeably except for parties.

There is no difference when you're talking about a party or another event, but both words have many other meanings, too.