Place cover on and insert the air lock. Put water in the air lock and attach its cover. Bubbles will start passing through the airlock in a day or so. Fermentation is over when the bubbles slow to 1 every 5 min. This can take 4 to 14 days.
Some people believe in boiling all water and then letting it cool over night.
They say this sanitizes the water. I run mine through a charcoal filter and have never had any problems. Manchester, NH tap water is very good water. Anything out of a well may have to be boiled and iron should also be removed. The main reason you have a plastic fermenter and a glass carboy is that a lot of people ferment in two stages.