It has been bugging me for a very long time and I'm really sick of it. For example there's a script called testscript that compares two directories. In class the prof can just type

testscript dir1 dir2 

to get the output, but I have to add ./ before the testscript and hit enter. Then enter dir1 and dir2 next line

How did the prof do that? Is it something with the bashrc thing? I never get how it works. If it's related please explain in plain simple language since I'm new to Linux. Thank you!