How to connect 2 faces? I am new to blender, and tried to make my sword based on my mind. And I found a problem...

I want to connect the center/middle cube to the lower sword part(the small gap between the sword), but I don't know how. I tried to connect it, but it will be intersect with each other and unable to delete the area inside it(at least I tried). I tried to use boolean method, but it  got an error(might be my drawing's problem). Can you teach me how to fix/do it?
In Edit mode, and on edge mode, select the edges you want to create a face with and hit the F key.