All of the data fitting tabs (Volume, a, b, c, UVW/hkl) have the same functions.
All that differs is which data they handle. If the data is not present in your dataset, then the corresponding tabs will be inactive.
In each data-fitting tab you can fit up to three different EoS. Select them with the EoS buttons.
The release of 2021 has an improved Estimation procedure that is faster, more reliable, and allows the user to control which parameters are estimated:
The normalized parameters tab does not perform any fitting, it is only a display feature that allows for quick comparisons among different lattice parameters and crystallographic directions.