1) 1 : to bring or come to an end : complete. 2 : to use up completely I finished the pie. 3 : to end a competition in a certain position I finished third in the race. 4 : to put a final coat or surface on He finished the wood table with varnish.
2) Completely is an adverb that comes from the Latin completus, "to fill up." We use it to mean "entirely" or "wholly." So if a building is completely destroyed, no part of it is left standing. Reading a newspaper story or watching a documentary film completely means you finished it from beginning to end.