A complex sentence is a sentence consisting of an independent clause and a subordinating clause. Or, to put it more simply, complex sentences involve more than just a straightforward noun + verb. Complex sentences include extra phrases added to a base sentence, but which cannot stand alone as a sentence. For example:
Published 4:00 am, Thursday, January 9, 1997. 1997-01-09 04:00:00 PDT Yosemite National Park -- Yosemite Valley is slowly drying out after what park rangers are calling the worst flood here in recorded history, leaving behind hundreds of upturned tent-cabins and acres of wrecked camping sites.
Camping in Yosemite is one of the best ways to experience the park. There are 13 campgrounds in Yosemite National Park with 1,445 total campsites. Roughly 1,000 campsites can be reserved in advance. The rest are first-come, first-served. During peak season (June, July, August) Yosemite camping can be challenging because campgrounds in the park fill up fast.