I'm trying to draw (chalk) a starting line.
I have my level and T square but I can't seem to figure out how the level works to get a straight line on the floor or to determine if a wall is straight. The level only seems to be detecting the levelness of the floor itself (if that makes sense).
I'm sure our walls are not level and there are dips and angles (not 90 degrees).
Any trick to doing this?

I don't even know what to say about this, except you should hire a professional.

Thanks for your suggestion, but not going to happen.
Our house is just full of inaccurate angles, as most homes are. and I want to start with the straightest line.
Maybe my brain is too full of dust at this moment. And I think I'm over-thinking this.
I'll go in again soon and try again.

Try hiring an inspector, he might be able to figure it out...someday. lol


Seriously though, outside walls are generally the straightest. However if you have a hally the outside wall may not correspond to that wall line in the hall. You may need to snap a couple lines and ajust to what looks best.

I use a laser square alot

On my website slideshow (front page lower level) you can see me lining up a row on a job I went back to, to add more rooms. I wanted the lines/rows to look perfect.

If possible, post a diagram, that will help for suggestions. I've never used a level or a T-square for layout. Basically I use a method of chalking lines from certain points, measurements, and layout of focal points. I need to visualize the layout and take it all into consideration.

I like visuals too. I decided to do two chalk lines crossing each other (centers of the room from each side) then taking the distance from the center (where the two cross), minus the expansion, and marking that measurement on each side (each end).
I think that will work.
I know nothing is perfect, but trying my best.

What you want to do is take an equal measurement off of either end of the wall you want to start off of and make a mark on the subfloor then use an actual chalk line to snap a line between those 2 points that will be your reference point for straightness.

That's exactly what I did. I also figured out that when the boards that were installed, they were installed perfectly aligned as well so I was also able to confirm the measurements off those boards.
The wall does curve in and out (outside wall) where we are going to start installing at.
I'm not surprised. This also happened with all of our past tile projects.