What do builder houses actually do? Are builders different than "free workers"?

[Malaris]

I build 2 builders houses, but each morning as my population expands i have 20 free workers. Expand my housing and i have like 50 free workers. How do builder houses factor into the overall workforce of my empire?

I ask because i initially thought i had to build 20-30 builder houses to get free workers to make troops, staff buildings etc. But It seems i just need to build a few builder houses and more regular housing and my free worker population grows. Can anyone help clear up my confusion on this likely simple mechanic im having trouble understanding

[NitoriTheKappa]

Builder houses turn free workers into the people who actually build and repair things. They do not contribute to your population. Your free workers just loaf around and eat food until you give them something to do.