Trying to advance a bit and need some explanation

While trying to find a partial mash hefeweizen I keep seeing recipes from beer software programs like beersmith with a section as follows:

Name Description Step Temp Step Time
Mash In Add 3.50 gal of water at 165.9 F 154.0 F 60 min
Mash Out Add 3.00 gal of water at 196.6 F 168.0 F 10 min

So am I correct to assume the initial mash (grain bag for me) would be whatever the grain bill is + water @ between 154-165.9 and steep for 60 mins and then remove grain bag and add bag to another 3 gallon pot of water between 168-196.6 for 10mins. Then combine both pots + whatever the extract is and boil.

Yeah more or less. Have you read the Partial Mash Sticky?

https://www.homebrewtalk.com/f39/easy-partial-mash-brewing-pics-75231/

no, what it is saying is that you add 3.5 gallons of 165.9 degree water to X pounds of grain, and the mixture will reach an equilibrium of 154 degrees. you mash at that temp for 60 minutes.

then you add 3 gallons of 196 degree water. the mixture will reach an equilibrium of 168 degrees, and you mash out at that temp for 10 minutes.

you should get a good intermediate level book that has a chapter about mashing. that's what's being described there. the numbers 154 and 168 should jump out at you.

Not quite, you have water at 165.9 which you mix with your grain ending at 154.0 (ie the grain will cool the water somewhat). Leave it for an hour then add water at 197 to your existing mash ending at 168.

I'm slightly surprised there isn't a third sparge step which, for BIAB, would usually mean a transfer to another pan of water.

Oh, I read the question too quickly. Still a good link for what you are doing though.

I have read the Intermediate section of"The Joy of Home Brewing" several times and the sticky but could not find the process or terms "mash in" or "mash out" Its alot info to digest as I am finding there are several ways to skin a cat, so I am asking questions as they come up. And I dont remeber seeing those numbers, but I assume they are the temp range for conversion. I believe I read nothing above 170 for mashing somwhere.

Anyway so for clarification are the terms "mash in" & "mash out" processes or generic terms?

Sorry just trying to get a handle on some stuff. Thanks for the patience and explanations!