Answer
Statically determinate beams are those beams in which the unknown reaction forces are equal or less than the equilibrium equation.
As shown in figure 1 in which reaction forces are 3 and we have 3 equilibrium equation so beam is determinate.
Statically indeterminate beams are those beams in which unknown reaction force are more than the  equilibrium equation.
As shown in figure 2 in which reaction forces are 6 and we have 3 equilibrium equation so beam is indeterminate.
