This is the 953rd most frequent Russian word.
сложно
"Сложно" means "difficult" or "complex."
In this sentence, 'сложно' is used as an adverb to describe the level of difficulty of navigating a location.
Здесь слишком сложно ориентироваться.
It's too difficult to navigate here.
Here, 'сложно' functions as an adverb modifying the verb to imply that the style of explanation was complex and challenging to follow.
Он объяснил задачу так сложно, что никто не понял.
He explained the problem so complicatedly that no one understood.
In this example, 'сложно' is used adverbially to indicate the challenging nature of completing the task within the given timeframe.