This how-to assumes you have basic brewing equipment and skills. BIAB is simple and a great way to step into all-grain home brewing!
Collect full volume of water and start heating to strike temp- this method requires no sparge. For a typical 5 gallon batch you will collect between 7-9 gallons of water.
Measure out and mill your grain while water is heating. Your local homebrew shop will do this for you.
Move milled grain into large grain bag (24" x 24")- I bought mine for about $6 at www.morebeer.com
Once your water reaches strike temp, usually 6-8F higher than intended mash temp, place bag of grains in kettle and stir thoroughly. Small clips can be used to secure top of bag to rim of kettle.
Place lid on kettle and insulate mash tun to reduce heat loss using heavy blankets, a sleeping bag, or towels. Let grains mash for 60 minutes.
Have a homemade beer while waiting for mash to finish.
After 60 minute mash is complete, raise temp of mash to 168F for mash out. Then remove grain bag and squeeze it to extract as much wort as possible.
Bring wort to a boil and proceed like any other batch of beer (i.e., hop additions, etc).
Have another homemade beer during boil.
To reduce hop matter in the kettle, these paint strainer bags work great... and they are cheap! Simply put all hop additions in the bag, which remains in the boil kettle.
With 15 minutes left in the boil, add Irish Moss/Whirlfloc to boiling wort and sanitize whatever chiller you use via boiling wort (I use a pump and plate chiller)
After the boil is complete, chill wort to pitching temp and transfer to fermenter. I use a sanitized paint stir rod (with cordless drill) to aerate.
Pitch yeast, place fermenter in a temperature controlled area, and let it ferment.
And that's all there is to brewing all grain Brew In A Bag! There are numerous versions of this process, but this will get you great beer, simply. And it only took 4.5 hours. Cheers!