your module is not installed on you machine.
the way you have created is meant for the CPAN

create a file say Testingmodule.pm (note the extention .pm)
and then in the same directory
create you program and write use Testingmodule
OR
you can upload your module to CPAN and then install it on your machine perl -MCPAN -e 'install youmodulename'and then use it in your program
because by installing it, itll come to @INC.
but this is not a good idea since your module is not be usefull to anyone
use CPAN to share usefull module
OR
install it by source i.e
perl Makefile.pl
make
make install

I Hope Everything is clear now