1- radiation buondry means the space that you should define as a farfield area and make it as an radiation , so your device can radiate in far field. thid area should be more than 10*lambda
2- to calculate the equations, HFSS has some passes, if the difference between two results in each passes is less than for example 0.02 (that yourself define it), the calculation finished. if not, untill number of passe that you yourself define, the calculation will stop.
3- frequency sweep means the range of frequency that our model will simulate on all of that frequencies with step size that you define.
4-add trace used for see two or more graphs in one figure.