He swam slowly and falteringly.
verb adverb 1 adverb 2
He rode determinedly and swiftly.
He laughed loudly and heartily.
A double ly ending sentence ends with two adverbs.
The first part must end with a verb, eg:
The worried people ran.
You make it more exciting by adding two adverbs on the end to describe how they ran.
The worried people ran quickly and purposefuly.