Every time I open a file 'Open With' comes up I'm sick of it please help?

Alright so everytime I try to open a file a thing-a-ma-jig always pops up and says 'Open With' so I have to search for whatever i'm wanting to open. I want to know how I can fix this so everything is normal again. I've read alot of options for getting rid of this but don't understand whentever it is whoever is trying to explain, hahaha I'm stupid. So yeah hel please, I have an Acer if that makes any difference :D