I don't understand Character Styles!!

I've tried to use character styles many times, and usually get so frustrated and give up. But I really want to figure this stuff out so that I can use these useful little tools properly!! Here is what I'm struggling with right now:

I have a text box with text size 29.45 pt in it. If I click on this text and select it and create a new character style, I get a character style that is 52 pt, not 29.45 pt as the text is appearing.

If I instead select that text and click on the "clear override" button, the text changes to another font altogether and is now 3.37 pt.

What??

I decided to just start over. I created a new text box with size 29.45 pt text. I selected the text and created a new character style and named it "Slider Heading". In the settings, I can see that the size set for this new character style is set to 29.45, just like I want.

If I make a brand new text box and apply my "Slider Heading" character style, it works!

But if I select the text I've been working with already and select "Slider Heading", nothing happens. A little plus sign appears next to its name though. I tried clicking the "clear overrides" button. This changes the text to 16.52 pt. That seems random to me... If I try to again click on "Slider Heading", nothing happens and the little plus sign next to the name is gone.

I don't understand!!! I hope someone does. Please impart your wisdom upon me!