Does anyone know how use a value from keyword test A and use it in test B, also when updated in A?

In Test A, use the operation "Set Variable Value" to create a variable on the Project level that contains the desired value you want to pass over to test B.  

Then, in Test B, whatever operation you are wanting to use the value in, there should be a parameter of some sort.  That parameter has a "mode".  Set that mode to "Variable" and then select the project variable.