Average input current in forward converter
Switching converters convert power.
So if a load is 10V @ 1A that's 10Watts.  Now the input side will take that same 10Watts but at a different current and voltage.
Maybe you have 120V input, then that is
\$\frac{10W}{120V}=0.0833A\$ input current.
All of this neglected efficiency.  So adding that in: at 80% efficiency the input power is \$10W*1.2=12W\$.
Going back to calculate current now gives \$\frac{12W}{120V}=0.1A\$ input current.