Start typing and the timer starts with you. When the passage ends you get two numbers: words per minute, and the share of characters you got right. Retake it as often as you like — there is no signup and no limit.
A "word" here is five characters, including spaces. That convention is what makes scores comparable at all: without it, a test full of short words would flatter you and one full of long words would not. Every typing test worth trusting uses the same definition, so a score from this page means the same thing as a score from anywhere else.
Accuracy is the number to watch, not speed. Correcting a mistake costs the time to notice it, the backspace, and the retype — so typing at 60 WPM cleanly beats typing at 80 with errors. If you are practising, slow down until you are above 97% and let the speed come back on its own.