Typically "freaking" would be used to express emphasis, frustration and/or annoyance. It's informal and I wouldn't recommend using it around people you respect.

Like , this is freaking awesome !! :D

It replaces a much stronger swearword ending in -ing. It's a modern word, more common in the USA than the UK, and is used mostly by young people. If you lived in America, you might get the feeling for when to use it naturally, after some time.