I'm new to this and my Math skills are .... suspect sometimes.
I have 2 operations maybe more I'm trying to get to work, in Excel i get the formula to act as expected but cant do the same in the blocks.

Any ideas?
My1st formula
Hollow Grinding Height Calculator. Please enter the Diameter of the Contact Wheel (D), Material Thickness (T) & Edge Thickness (E) in mm & the maximum bevel height will be Calculated.
Formula: H = √((D÷2)² - ((D÷2) - ((T-E)÷2))²).

From Excel is =SQRT((A3/2)^2-((A3/2)-((B3-C3)/2))^2)

That makes sense but now... on my Screen I have 3 Cells for input values & then the Answer Cell.
So D, T & E are number only values the user will input, H would be the answer.
Trying to initialize... the app wont work... I can input any number i like but the formula is not actually running.

Sorry, but I can't understand your issue.
Is your screen showing the Blocks button, or not ?
Have you implemented what @TIMAI2 has said ?
Before trying further attempts probably you can find some hints here: https://appinventor.mit.edu/explore/ai2/beginner-videos
Or post your .aia